ASHINGTON, Oct. 9 ?Attorney General John Ashcroft set up a "9/11 Task Force" within the Justice Department today to operate as the agency's central command structure for prosecuting terror cases and helping to prevent further acts of violence against the United States, a senior department official said.

Mr. Ashcroft's decision is a significant shift for the Justice Department, reflecting his increasingly aggressive managerial approach since the attacks and the consolidation of his control over federal law enforcement's antiterrorism efforts.

Moreover, the decision is, in effect, a rebuff of Mary Jo White, the United States attorney in New York who operated during the Clinton administration as the country's pre-eminent prosecutor of terror cases and one of the government's most prominent leaders on antiterrorist efforts.

Under the new organization, Ms. White's office would remain involved in prosecution decisions and efforts to prevent terror attacks, but overall decision-making would rest firmly with Mr. Ashcroft in Washington.

Previously, attorneys general have granted prosecutors in the 92 United States attorneys' offices wide discretion in handling criminal cases, a latitude that the new structure now ends where terrorism is concerned .

Today, the senior law enforcement official said that Mr. Ashcroft had set up "a structured prosecution team" to handle cases involving the attacks on the World Trade Center and the Pentagon.

It will be made up of government lawyers from United States attorney's offices in New York and Virginia, as well as prosecutors from the Justice Department's violent crime and terrorism unit.

The new prosecution team will be in charge of gathering leads, information and evidence from around the world to centralize the effort to head off future terror attacks. The team will also be responsible for any prosecutions that would result from the investigation, including the place and timing of any indictments.

Mr. Ashcroft advised his senior aides of his decision at a meeting today. Among them were Larry Thompson, deputy attorney general, and Michael Chertoff, the department's chief criminal prosecutor. Also at the meeting were Ms. White and Paul McNulty, the United States attorney in eastern Virginia, whose jurisdiction includes the Pentagon.

At issue is more than a fight for prestige for prosecutors in New York. Some prosecutors have said that the effort should be centered in New York, because it suffered thousands of deaths along with untold economic devastation.

It is still uncertain if any major indictments or prosecutions will result from the investigation. The 19 known hijackers are dead and a senior law enforcement official said today that, thus far, no one had been identified in the United States as a witting accomplice. Moreover, the official said, investigators are still trying to determine the role of suspected conspirators overseas.

In part, today's decision reflects the changing fortunes of Ms. White, who was appointed in 1993 by former President Bill Clinton shortly after the first World Trade Center attack. Mr. Ashcroft has kept her in her post, but he has not given her the same latitude that she had under Janet Reno, the attorney general during the Clinton administration.

Ms. White, who has tried to retain her independent role in terrorism issues, made two core arguments for keeping control over future criminal indictments of possible defendants tied to Al Qaeda, Osama bin Laden's terror network, one official said.

First, thousands of victims were killed in Lower Manhattan, which is within Ms. White's legal jurisdiction, the Southern District of New York.

Also, Ms. White's office has a long track record on terror cases. Her prosecutors have already obtained 10 criminal indictments of Mr. bin Laden and his followers, starting with one for terrorism conspiracy in June 1998, two months before the bombings of the American embassies in East Africa.

Ms. White's spokesman, Marvin Smilon, had no comment last night.

But one official said that Ms. White's office delivered a substantial briefing package to the attorney general's office, arguing to preserve New York's legal jurisdiction.

In the case of the Sept. 11 attacks, an official said, Ms. White made the argument that "she still has the responsibility to preserve the rights of the victims because federal laws were violated within the jurisdiction of the Southern District."