Pre-9/11 Files Show Warnings Were Dire and Persistent

The commission's chairman, Thomas H. Kean, a Republican, has described failures at every level of government, any of which, if avoided, could have altered the outcome. Mr. Kerrey, a Democrat, said, "My conclusion is that it could have been prevented. That was not my conclusion when I went on the commission."

It was not until Sept. 10 that Mr. Bush's national security aides approved a three-phase strategy to eliminate Al Qaeda. The plan, which was to unfold over three to five years, envisioned a mission to the Taliban in Afghanistan, where Al Qaeda was based; increased diplomatic pressure; and covert action. Military strikes might be used, but only if all other means failed.

"I don't see any evidence that our airports were on heightened alert," he said. "A hijacking was not a bolt out of the blue."