In an appearance before the Senate Intelligence Committee, Mr. Tenet offered a sobering assessment of the threat al-Qaida still poses to the United States and its allies.

"We have time and again uncovered plots that are chilling: On aircraft plots alone we have uncovered new plans to recruit pilots and to evade new security measures in Southeast Asia, the Middle East and Europe," he said. "Even catastrophic attacks on the scale of 9/11 remain within al-Qaida's reach. Make no mistake, these plots are hatched abroad, but they target U.S. soil and those of our allies."

Al-Qaida is blamed for the September 11, 2001 attacks on New York and Washington.

Mr. Tenet noted the United States had captured several members of al-Qaida's leadership. But he said the spread of the organization's ideology ensured a continuing threat.

The CIA director said the steady growth of anti-U.S. sentiment among Sunni extremists and what he called 'al-Qaida's destructive expertise, ensure that a serious threat will remain for the foreseeable future, with or without al-Qaida in the picture'.

Also testifying Tuesday was the Director of the Federal Bureau of Investigation, Robert Mueller, who said terrorists are intent on damaging the U.S. economy and U.S. prestige. He said al-Qaida is intent on attacking U.S. transportation systems, and would revisit targets missed in the past, including the White House and the U.S. Capitol.

A hijacked plane that crashed into a Pennsylvania field on September 11, 2001 was believed to have been destined for the White House or the Capitol building.

Meanwhile, CIA Director Tenet came under fire from Democrats, who criticized pre-war intelligence about Iraq's weapons of mass destruction.

Mr. Tenet's former special adviser, David Kay, left his position as top U.S. weapons inspector, telling Congress a month ago he does not believe weapons of mass destruction will ever be found.

"When we send our military out and find nothing, and then Dr. Kay goes over and finds nothing, for the intelligence community I guess you believe something is going to materialize," said Senator Dianne Feinstein, a California Democrat. "In terms of weaponization and deployment, and then finding nothing, it is a pretty bitter pill to swallow with respect to the value of intelligence."

Mr. Tenet defended the work of his intelligence analysts, and said the search would continue for weapons of mass destruction in Iraq. "They believe what they wrote. They did not do it cavalierly, and they did not do it frivolously, and they believe they had a connective logic, and a tissue to get them to their judgments. I believe you have to keep working and looking," he said. "I believe you have to know whether this material may have slipped over a border or fallen into somebody's hands, or used by insurgents against us at some point. We have a responsibility to keep doing this."