ASHINGTON, Feb. 6 ?George J. Tenet, the director of central intelligence, said today that Al Qaeda was trying to reconstitute itself and remained capable of another large- scale attack against the United States.

While many Al Qaeda leaders are still at large, nearly 1,000 operatives have been arrested or detained since Sept. 11 in about 60 countries, seriously disrupting the network, Mr. Tenet said in his first public Congressional testimony since the terrorist attacks. That figure is much larger than officials have stated previously.

But Al Qaeda is now trying to rebuild its network and resume its operations, Mr. Tenet warned. While a number of Al Qaeda plots have been disrupted, he said American intelligence officials knew that Al Qaeda had considered attacks against high-profile landmarks, government targets, airports, bridges, harbors and dams. The network also has plans to attack American and allied targets in Europe, the Middle East, Africa and Southeast Asia, he said.

"Operations against U.S. targets could be launched by Al Qaeda cells already in place in major cities in Europe and the Middle East," Mr. Tenet said. "Al Qaeda can also exploit its presence or connections to other groups in such countries as Somalia, Yemen, Indonesia and the Philippines."

"I must repeat that Al Qaeda has not yet been destroyed," he said.

In Afghanistan, Mr. Tenet said, the United States had recovered documents that showed that Osama bin Laden was pursuing a sophisticated biological weapons research program. He said the group was also trying to acquire dangerous chemical agents and toxins, as well as a weapon that would disperse radioactive materials.

He said that he was uncertain whether Mr. bin Laden was still alive, but that the Central Intelligence Agency believed that Mullah Muhammad Omar, the Taliban leader, was alive.

Mr. Tenet also told the Senate Select Committee on Intelligence that some Al Qaeda members were seeking refuge in Iran, while elements of the Taliban, along with pockets of Arab fighters still in eastern Afghanistan, continued to threaten the interim government of Hamid Karzai and international efforts to rebuild the country.

The counterterrorism chief of the Federal Bureau of Investigation, Dale Watson, appeared with Mr. Tenet and other intelligence officials before the intelligence committee in a wide-ranging review of terrorism and other threats to the United States.

Mr. Watson said the F.B.I. had found evidence that Richard C. Reid, the British citizen arrested in December after he tried to ignite explosives in his shoes while on a trans- Atlantic flight, was an associate of Zacarias Moussaoui. Mr. Moussaoui, a French citizen, was detained in Minnesota in August, after a flight school raised suspicions about him with the F.B.I. Mr. Watson also said the evidence now suggested that Mr. Reid was affiliated with Al Qaeda.

In what amounted to a warm-up for future Congressional hearings on the government's failure to predict or prevent the Sept. 11th attacks, Senator Richard C. Shelby of Alabama, the ranking Republican on the intelligence panel and Mr. Tenet's most vocal Congressional critic, pointedly asked the C.I.A. chief to explain what he called an intelligence failure on the scale of Pearl Harbor. "The U.S. has an intelligence community today, and a director of central intelligence, in large part because of the Pearl Harbor disaster of December the 7th, 1941," Mr. Shelby said.

"The fear of another Pearl Harbor provided the impetus for our establishment of a national-level intelligence bureaucracy," he continued. "This system was created so that America would never have to face another devastating surprise attack. That second devastating surprise attack came on September the 11th."

He added, "All of us, I think, owe the American people an explanation as to why our intelligence community failed to provide adequate warning of such a terrorist attack on our soil."

Mr. Tenet challenged the assumption that there had been an intelligence failure. "We welcome the committee's review of our record on terrorism." he said. "It is a record of discipline, strategy, focus and action. We are proud of that record."

He added that "when people use the word `failure,' `failure' means no focus, no attention, no discipline, and those were not present in what either we or the F.B.I. did here and around the world."

Mr. Tenet added that the C.I.A. received numerous reports last spring and summer about possible attacks against American interests, and suggested that the reports might have been related to what turned out to be the World Trade Center attacks. "Intelligence will never give you 100 percent predictive capability on terrorist events," he said.

Mr. Tenet also said Mr. bin Laden did not believe that the United States would respond to the Sept. 11 attacks by attacking Afghanistan. He "did not believe that we would invade his sanctuary," he said, adding: "He did not know about the collection and operational initiatives that would allow us to strike with great accuracy at the heart of the Taliban and Al Qaeda. He underestimated our capabilities, our readiness and our resolve."

In Mr. Tenet's review of other global threats, he described Iran ?one of three nations identified by President Bush in his State of the Union address as points on an "axis of evil" ?as the world's leading state sponsor of terrorism. Mr. Tenet said that the reformist political movement in Iran seemed to be losing momentum, and that Tehran's security forces, under the control of fundamentalist clerics, appeared "bent on countering the U.S. presence," in Afghanistan.

He also said Iran's involvement in a shipment of arms to the Palestinian Authority, seized by Israel, "probably was intended to escalate the violence of the intifada and strengthen the position of Palestinian elements that prefer armed conflict with Israel."

Iraq, also cited by Mr. Bush, continues to pose a threat to the United States as it develops chemical and biological weapons. "Baghdad is expanding its civilian chemical industry in ways that could be diverted quickly to chemical weapons production," Mr. Tenet said. "We believe it also maintains an active and capable biological weapons program."

He also said the government of Saddam Hussein had "never abandoned" its efforts to develop nuclear weapons.

North Korea, the third member of Mr. Bush's "axis," is exporting components and completed ballistic missiles to other countries, Mr. Tenet said, adding that it was using the profits to support its own missile program, and probably covert efforts to develop weapons of mass destruction. It can then turn around and "generate new products to offer to its customers, primarily Iran, Libya, Syria and Egypt," he said.