Mr. Tenet told the panel U.S. intelligence sources "lit up" in the weeks before the terrorist attacks on New York and Washington.

The CIA director says, however, the warnings were "maddeningly short on actionable details."

He says intelligence indicated an attack would occur overseas, especially against U.S. interests in the Middle East.

Mr. Tenet says he does not believe the September 11 attacks could have been prevented if al-Qaida leader Osama bin Laden had been killed or captured before 2001 because plans for the terrorist plot were already established.

He says the United States is now in a better position to counter terrorism.

"As a country you must be relentless on offense, but you must have a defense that links visa measures, border security, infrastructure protection and domestic warnings in a way that increases security, closes gaps and serves a society that demands a high level of both safety and freedom. We collectively did not close those gaps rapidly or fully enough before September 11," said Mr. Tenet. "We have learned and are doing better in an integrated environment that allows us to respond faster and more comprehensively than three years ago and much more work needs to be done."

Speaking before members of the commission, and with families of victims of the September 11 attacks in the audience, Mr. Tenet says he is concerned as years go by that some people will believe the danger from future terrorist attacks has diminished.

The CIA director says terrorists are still plotting to kill Americans and predicted more assaults in the future.

"As this thing fades my fear is that people are going to say it's five years away," he said. "It is not. It is coming. They are still going to try and do it. We need to, men and women here that have lost their families have to know, we have got to do a hell of a lot better."

Also testifying before the commission Wednesday is former White House counter-terrorism official Richard Clarke.

Mr. Clarke has written a book alleging that President Bush paid too little attention to al-Qaida before the September 11 attacks, and focused too much on a possible link with Iraq.