ASHINGTON, May 8 — The orders that sent most of the 320th Military Police Battalion to Iraq came on Feb. 5, 2003, as part of the tide of two-week-a-year soldiers being called up from the National Guard and the Army Reserve in preparation for war.

In theory, the battalion's specialty was guarding enemy prisoners of war, a task that was expected to be a major logistical problem. In fact, an Army report said few of the 1,000 reservists of the 320th had been trained to do that, and fewer still knew how to run a prison. They were deployed so quickly from the mid-Atlantic region that there was no time to get new lessons.

"You're a person who works at McDonald's one day; the next day you're standing in front of hundreds of prisoners, and half are saying they're sick and half are saying they're hungry," remembered Sgt. First Class Paul Shaffer, 35, a metalworker from Pennsylvania. "We were hit with so much so fast, I don't think we were prepared."

The battalion — including insurance agents, checkout clerks, sales people and others — ultimately would follow a grim trajectory into the episodes of prisoner abuse that have shocked the nation. The soldiers found themselves in charge of Abu Ghraib prison in Iraq at a time when the increasing rage of the anti-American insurgency, along with the desperation of American commanders to glean intelligence, magnified the pressures on the unit. This account of the troubled battalion is based on interviews with soldiers, their relatives, military commanders and Army reports.

Within days of the American invasion of Iraq, the 320th was in Kuwait, and the unit moved swiftly into southern Iraq, first to a prisoner of war camp overseen by British troops and then to a sprawling barbed-wire American camp in the desert. Known as Camp Bucca, the American camp was home to a legion of Iraqi prisoners.

"We were supposed to be the experts on this, but all we knew is what we learned in our summer camp," said Scott McKenzie, 38, of Clearwater, Pa., a sergeant first class who has since been discharged from the service. "We never learned how to deal with a riot, what to do when we were being assaulted."

On May 12, Mr. McKenzie, who worked in civilian life as a guard in a boot-camp style detention center, was escorting some Iraqi prisoners at Camp Bucca when just such a riot broke out, in what became the first incident of prisoner abuse involving the unit. At least one detainee was held down while Mr. McKenzie and two other soldiers badly beat and kicked him, according to testimony presented in a court-martial. This was done at the urging of a superior, Master Sgt. Lisa Girman, according to the testimony.

"We called it just another night in the desert," Mr. McKenzie recalled last week. He insisted that he had used no more than "the minimum force necessary to regain control of the prisoners" and that the event was "no big deal."

Mr. McKenzie, Ms. Girman and another soldier were found guilty of mistreating Iraqi detainees, and they accepted a less-than-honorable discharge in a plea bargain. A fourth soldier in the unit also was granted a less-than-honorable discharge separately. But the incident prompted no effort by the soldiers' commanders to make sure the abuse was not repeated, according to an Army investigation by Maj. Gen. Antonio M. Taguba into the maltreatment of prisoners. The inaction was a lapse in leadership that reflected the eventual near total-breakdown of discipline in the unit.

Many members of the 320th had expected their mission to wind down once Iraqi prisoners were freed, after the declaration on May 1, 2003, that major combat operations had ended. Instead, to their considerable disappointment, the soldiers learned that they would be sent on to longer missions.

Some elements of the battalion were still coming in, including the 372nd Military Police Company, based in Cresaptown, Md., which arrived in May 2003. At first the 180-member company was assigned to work with marines in the southern town of Hilla. With a specialty in law enforcement, the company was ordered to help train a reconstituted Iraqi police force in Hilla.

Under Lt. Col. Jerry L. Phillabaum, most of the battalion was directed to a different destination.

With the P.O.W. facilities at Camp Bucca, the Baghdad airport and other sites still crowded, and the processing of prisoners taking time, the Army was looking for more permanent detention quarters.

Just as the occupation authorities turned to Saddam Hussein's old palaces to house the new Coalition Provisional Authority and other American headquarters around the country, they chose as the new American prison Mr. Hussein's old one at Abu Ghraib, even though it had a history of executions and torture that made the prison one of the most feared symbols of the old government.

Mr. Hussein had emptied Abu Ghraib of its occupants in October 2002, in a gesture aimed at winning popular support and possibly at stirring trouble for any American occupation. As late as June 2003, its gates were still adorned with his portrait.

Once the Army decided to reopen the 280-acre site, it did so swiftly, renovating cells, painting the walls and sweeping up broken glass and other debris left from months of looting. In July, much of the 320th Battalion was sent to Abu Ghraib. The reservists were turned into wardens of what was to become the world's largest prison run by the United States Army.

The New Wardens
A Rebellion Begins, and a Prison Reopens

At the outset of the American occupation, Abu Ghraib held only about 2,000 Iraqi prisoners, most housed in tents erected under the scorching summer sun outside the prison itself.

The inmate population grew quickly, as prisoners arrested after the war emerged as a far bigger challenge than those taken in the war.

"We were real short-handed," said Sergeant Shaffer, the metal worker from Pennsylvania, who described cases in which no more than six guards on a single shift would be in charge of 700 Iraqi prisoners. "On my compound, we were doing 16-hour days. It was a very high-stress environment."

There were also clear clashes of culture, as soldiers who had little knowledge of the Middle East found themselves frustrated by the poor conditions, the prospect of a yearlong deployment and a lack of compliance among the Iraqi prisoners.

"They don't want to listen," Sergeant Shaffer said. "We'd say we want you to line up at 9 o'clock; they'd say, `If you want us to line up at 9 o'clock, we want something in return.' It doesn't work that way."

Among the prison's new inmates, many were criminals, some of the same ones freed by Mr. Hussein. When they joined in the looting, lawlessness and other crimes, the Americans rearrested them.

But a more worrisome category of prisoners emerged from the widening insurgency in Iraq, as played out in the shootings, bombings and other attacks against American soldiers. More and more of those prisoners were filling the makeshift jails.

In addition to Abu Ghraib, they included Camp Bucca in the south; Camp Cropper, a high-value prisoner center near the Baghdad airport; and Camp Ashraf, a former camp for the Iranian opposition group Mujahedeen Khalq, which was being used to detain its members. The facilities were overseen by the 800th Military Police Brigade, with headquarters in Uniondale, N.Y., the 320th Battalion and the much smaller 372nd Military Police Company from Maryland.

Various Army divisions and other military units also maintained detention facilities around the country where they could hold prisoners for as long as 14 days before transferring them to other sites.

At Abu Ghraib, the prison was divided into three main subcamps. One, Camp Ganci, consisted of eight blocks of tents, each sealed off with razor wire and containing about 400 inmates in rows and rows of Army-issue canvas tents. Each tent held 25 inmates or more.

Camp Vigilant, another tent camp, was divided into four units with about 100 inmates each and was set aside for prisoners believed to have the most intelligence value.

Finally, there was the "hard site," the old prison itself, divided into seven blocks. Eventually, six were run by the Coalition Provisional Authority, for the detention of Iraqi prisoners to be tried in Iraqi courts. The seventh cellblock under American control, was divided into two parts, 1-A, set aside for "high risk" prisoners, and 1-B, on the second floor, for female prisoners.

Together, the two parts had 103 cells, running down each wall, with a long corridor down the middle. Each cell — about 6 by 10 feet — had a bunk bed and a hole in the floor for a toilet. The cells were designed to hold 206 people.

From the initial 2,000 prisoners, the population skyrocketed toward 7,000 prisoners by September as thousands more "security detainees" were rounded up by soldiers on suspicion of involvement in attacks on American troops.

In Baghdad, a three-person team headed by Maj. Gen. Barbara Fast, the top American intelligence officer in Iraq, was in charge of reviewing the status of the security detainees as a prelude to their release. But far more Iraqis were being arrested than freed; the average stay in the prison was approaching four to six months. The 320th Battalion was stretched thin; working in temperatures that regularly exceeded 120 degrees only added to the strain.

Meanwhile, security conditions around the prison were worsening, with small-arms fire, rocket-propelled grenades and mortar fire coming into the compound almost every night. Colonel Phillabaum, the battalion commander, said that he and other officers dubbed the neighborhood around the prison "Little Mogadishu," after the Somali capital that in 1993 become a death trap for American soldiers. "The people just hated us," he said.

A Troubled Unit
Overcrowding and Prison Riots

By late in the summer of 2003, concerns about overcrowding, disciplinary problems and disturbances at American-run prisons in Iraq had reached the highest level of the military's headquarters in Baghdad. At Abu Ghraib in June, a riot broke out and eight detainees were shot, leaving one dead. Similar incidents occurred elsewhere.

But even more concern was focused on the mounting insurgency, and how little American intelligence had been gathered about it, even though thousands of Iraqis had been taken into custody. Mr. Hussein's two sons, Uday and Qusay, were dead, killed by American soldiers in July, but the former Iraqi leader was still on the run. Major bombings in August of the United Nations headquarters and at other sites added to the level of anxiety.

While military police were in charge of American prisons in Iraq, military intelligence units were in charge of interrogations. But changes were in the works.

Brig. Gen. Janis Karpinski, a business consultant and longtime reservist who had arrived in Iraq in late June to take over the 800th Military Police Brigade. "The numbers were increasing at rapid rates," she recalled in one of several television interviews this week.

"They were tagged as security detainees and they could not simply be released," she said. "They had to be interrogated, held, reviewed, and then ultimately released. I know that the interrogation, the interrogators, were under tremendous pressure."

In mid-August, a team of civilian interrogators led by Steven Stefanowicz, a former Navy petty officer and an employee of a Virginia company called CACI, began work at Abu Ghraib under a classified one-year military contract. The contract was part of a broader effort by the military to enlist Arabic linguists and other civilians in the work of questioning Iraqi detainees. CACI sent 27 interrogators to Abu Ghraib, Pentagon officials have said. Their job was to conduct interrogations in conjunction with military police and military intelligence units, according to a company memorandum.

Later that month, at the behest of senior Pentagon officials, Maj. Gen. Geoffrey D. Miller, the two-star Army general overseeing the American detention center at Guantánamo Bay, Cuba, was sent to Iraq. He was to review the American-led effort "to rapidly exploit internees for actionable intelligence," according to the Army report by General Taguba.

Among General Miller's classified recommendations, submitted after a tour that ended Sept. 9, were that the guards at Abu Ghraib and other facilities "be actively engaged in setting the conditions for successful exploitation of the internees," according to General Taguba's report.

At the end of September, Lt. Gen. Ricardo S. Sanchez, the top American officer in Iraq, sent his inspector general to Abu Ghraib. According to Colonel Phillabaum, the visiting officer told him, "You guys are the forgotten."

Isolated and without amenities like gyms and barbershops that were available to other troops in Iraq, morale in the 320th plummeted. Many reservists who had been sent home when their tours were complete had not been replaced, adding to the burden of the remaining guards even as the number of prisoners continued to rise.

Army doctrine calls for a military police brigade to handle about 4,000 prisoners. But a single battalion — about a third the size of a brigade — was handling 6,000 to 7,000 prisoners at Abu Ghraib. When battalion commanders sought to release hundreds of detainees deemed to be no threat to allied forces, they were blocked from doing so by officers in Baghdad, they have complained.

At the end of October, Colonel Phillabaum briefed General Sanchez on the deteriorating, dysfunctional conditions at Abu Ghraib. "It was a real heart-to-heart," Colonel Phillabaum said in an interview. "I told it the way it was."

Rocket-propelled grenades and small-arms fire were "a constant threat," General Karpinski said.

"Abu Ghraib was in the middle of a hostile fire zone," she said, adding that the unit was "mortared every night, practically." Within days of the briefing to General Sanchez, General Karpinski sent Colonel Phillabaum to Kuwait for two weeks "to give him some relief from the pressure" at the camp, General Taguba's inquiry found.

Colonel Phillabaum contends that General Karpinski was angry because his briefing reflected poorly on her command, so she began a process to reassign him to her headquarters. Colonel Phillabaum, however, returned to his post.

According to General Taguba, Colonel Phillabaum and his chain of command were part of the problem, rarely supervising their troops and failing to set basic soldiering standards for them or make them aware of the protections afforded to prisoners under the Geneva Conventions.

"Despite his proven deficiencies, as both a commander and leader," General Taguba concluded, General Karpinski allowed Colonel Phillabaum "to remain in command of her most troubled battalion guarding, by far, the largest number of detainees in the 800th M.P. Brigade."

In October 2003, the 372nd Military Police Company joined Colonel Phillabaum's battalion at Abu Ghraib.

In Hilla, they had seen little combat; in Abu Ghraib the soldiers suddenly found themselves under attack virtually every night from insurgents outside the prison.

In Hilla, the 372nd had been focusing on law enforcement. Staff Sgt. Ivan L. Frederick, one of the soldiers from western Maryland, for one, had spent six months working in operations, "manning radio's, mission board etc.," according to a journal entry he made on Jan. 24. In Abu Ghraib, however, unit members were assigned as prison guards, with responsibilities that included the so-called Tier 1 cellblock of the prison.

A few weeks later, on Nov. 19, 2003, General Sanchez made a surprising decision: he transferred formal command of Abu Ghraib to the 205th Military Intelligence Brigade under Colonel Thomas M. Pappas, a 32-year military veteran whose unit, based in Wiesbaden, Germany, had been assigned to the prison as the chief interrogators since it opened. Working with Colonel Pappas was Lt. Col. Steve Jordan, who headed the Joint Interrogation and Debriefing Center at the prison.

General Karpinski, Colonel Phillabaum and the military police in the battalion contend that the military intelligence officers had, even before Nov. 19, essentially taken control of the prisoners in the Tier 1 cellblock and had encouraged their mistreatment. General Taguba concluded that the 372nd "was directed to change facility procedures to `set the conditions' " for interrogations.

"It was like they were in charge now; it's a military intelligence unit now," said a member of the 32Oth Battalion, Sgt. John Lamela, of Wilkes-Barre, Pa.

The intelligence officers' practice of wearing uniforms without insignia made it difficult for soldiers to identify the officers or even to determine which of them were military and which belonged to other agencies, including the C.I.A., whose officers periodically visited Abu Ghraib prison to participate in interrogations.

"They were in charge; it was almost like whatever his battalion wanted, his battalion got," Sergeant Lamela said of one senior intelligence officer at the prison. "He moved people out of their units so his personnel could live in their units. His personnel could walk around without proper uniforms; we as M.P.'s were not to correct them; he would say, `Let it slide.' "

Sgt. First Class Joseph Mood of Benton, Pa., had a similar view of the intelligence officers' influence. "They took over the whole base; it was their show," he said. "That was their wording. `This is our show now.' They would try to get us to keep prisoners up all night, make them stand outside, have them stand up all the time — sometimes they asked the guards to do something that was totally against what you believed in doing."

An Open Secret
Reports of Abuse Trickle Out

During the summer and fall human rights groups in Iraq say they heard repeated complaints of prisoners being roughed up or abused by their American jailers. Those were not the only breakdowns of discipline in that period.

On three days, Nov. 5, 7 and 8, detainees escaped from the prison and Camp Ganci, according to the results of military investigations that have been made public. Then, in what appears to have been the worst of the incidents, a riot broke out on Nov. 24 in Camp Ganci in which 12 detainees were shot, and 3 of them killed, after members of the military police battalion opened fire. For reasons that have not been explained, nonlethal and lethal rounds were mixed in their chambers, according to the investigation.

Also at Abu Ghraib that month, an Iraqi detainee died as he was being questioned by a C.I.A. officer and a linguist who was working as a contract employee with the agency, in an investigation still under review by the agency's inspector general. Through December and January, there were more shootings, riots and escapes. The worst abuses at Abu Ghraib took place on or around Nov. 8, according to the details of the military investigation made public so far, and principally in Cellblock 1-A, the group of cells set aside for high risk prisoners.

It was largely in that cellblock that some guards from the 372nd are accused of committing abuses that General Taguba called "sadistic, blatant and wanton" criminal acts. Prisoners were punched, slapped and kicked and forced to strip naked and form human pyramids. Some were ordered to simulate sexual acts. In some of the photographs of the abuse that have surfaced in recent days, the M.P.'s are grinning.

Specialist Charles A. Graner Jr. is shown with his arms folded as he stands behind a pile of naked Iraqi prisoners; an unidentified Iraqi prisoner is seen hooded and standing on a small box, with wires attached to his body; and Pfc. Lynndie England is seen glaring down at a naked Iraqi prisoner, whom she is holding by a leash.

So far, seven enlisted soldiers from the western Maryland company face criminal charges, all from the incidents in Tier 1. But several inquiries are still under way, and the question of who was primarily responsible has still not been answered.

The report by General Taguba, though limited to the conduct of the military police, said that the general suspected much of the fault, either directly or indirectly, should be attributed to military intelligence units under Colonel Pappas and Colonel Jordan. Through a spokesman, Colonel Pappas declined to comment, and Army officials would not even say which unit Colonel Jordan is currently assigned to. General Tabuga also blamed Mr. Stefanowicz and another contractor, John Israel, neither of whom could be reached for comment.

General Taguba's inquiry also criticized commanders, including Colonel Phillabaum, for failing to supervise his troops and allowing a climate of abuse to take hold.

Colonel Phillabaum said he felt he was being made a scapegoat for the Army. "I have suffered shame and humiliation for doing the best job that anyone could have done given the resources I had to work with," he said.

Colonel Phillabaum pinned the bulk of the blame on two of of the 372nd's soldiers, Sergeant Frederick and Specialist Graner, who are both corrections officers in civilian life. Neither of the two have spoken publicly about the episode.

"These two people were really the ringleaders of this whole thing," Colonel Phillabaum said. "Everybody else followed."

They were the natural leaders in the military police company, he said, since they spoke of their work experiences.

"Taking these prisoners out of their cells and staging bizarre acts were the thoughts of a couple of demented M.P.'s who in civilian life are prison correction officers who well know such acts are prohibited," Colonel Phillabaum said.

He said the abuses that were photographed only occurred between 2 a.m. and 4 a.m., times that Sergeant Frederick and Specialist Graner knew no commissioned officers would be checking in. He said the digital photos are all time-coded, and they are all taken over a couple of weeks in this brief window.

"If they thought these acts were condoned, then why were they only done a few nights between 0200 and 0400 instead of during any time between 0600 and 2400 when there were many others around?" Colonel Phillabaum asked.

Sergeant Frederick's uncle, William Lawson, said his nephew had told him the soldiers were photographing the Iraqi prisoners at the direction of military intelligence officers as an interrogation tool.

"Somebody photographed the Iraqis with the intent of using those photographs to show new prisoners that came in, `This is what can happen to you,' to loosen them up psychologically," Mr. Lawson said.

In a letter to his family last year, Sergeant Frederick wrote that military intelligence officers encouraged mistreatment like confining naked inmates for three consecutive days without toilets in damp, unventilated cells with floors 3 feet by 3 feet. Inmates were also handcuffed to cell doors and forced to wear female underpants. "We have a very high rate with our style of getting them to break," Sergeant Frederick wrote to a relative, Mimi Frederick, in an e-mail message on Dec. 18, 2003, according to a copy of the communication. "They usually end up breaking within hours."

General Karpinski has also said that she believed the military police were "coached" in their abusive actions by military intelligence officers. Neal Puckett, General Karpinski's lawyer, said the military police "took all their instructions from military intelligence interrogators, who instructed them to bring the prisoners to and away from these interrogation facilities, and sometimes perhaps to soften them up."

He suggested that the interrogators had instructed the guards to "bring them back naked this time, leave them naked tonight, don't give them any clothes. We think that escalated over a period of time until it ended up in what we see in the pictures."

A military official said Saturday that some of the photographs in the custody of military investigators, but not yet publicly disclosed, depict military working dogs snarling and intimidating Iraqi prisoners. "There are photos showing military working dogs used in a threatening manner," said the official, who spoke on condition of anonymity. The official said he was not aware of when or at which prison in Iraq the photos were taken.

General Karpinski has complained that the initial investigation ordered by General Sanchez was limited to the conduct of her military police brigade and did not examine in any detail the role played by military intelligence and private contractors.

Not until General Sanchez received a preliminary briefing on General Taguba's findings on March 12, which identified the intelligence officers and contractors as having possibly been primarily to blame, did he order a similar review of any wrongdoing by military intelligence officers at the prison. For reasons that remain unclear, that inquiry did not begin until April 23.

"I'd like to know who was the one that was giving instructions to the military intelligence personnel to turn up the heat?" General Karpinski asked.

Nearly a year ago, when her troops assumed their prison duty at Abu Ghraib, the Army made a promise. When it reopened Abu Ghraib last June, soldiers hung a sign at the gate that proclaimed: "America is a friend of all the Iraqi people."

Thom Shanker in Washington, Kate Zernike and Michael Moss in New York, Dexter Filkins and Ian Fisher in Baghdad and Patrick E. Tyler in Wiesbaden, Germany, contributed reporting for this article.