The direct warnings to Mr. Bush about the possibility of a Qaeda attack began in the spring of 2001. By May 1, the Central Intelligence Agency told the White House of a report that “a group presently in the United States” was planning a terrorist operation. Weeks later, on June 22, the daily brief reported that Qaeda strikes could be “imminent,”although intelligence suggested the time frame was flexible.

But some in the administration considered the warning to be just bluster. An intelligence official and a member of the Bush administration both told me in interviews that the neoconservative leaders who had recently assumed power at the Pentagon were warning the White House that the C.I.A. had been fooled; according to this theory, Bin Laden was merely pretending to be planning an attack to distract the administration from Saddam Hussein, whom the neoconservatives saw as a greater threat. Intelligence officials, these sources said, protested that the idea of Bin Laden, an Islamic fundamentalist, conspiring with Mr. Hussein, an Iraqi secularist, was ridiculous, but the neoconservatives’ suspicions were nevertheless carrying the day.

In response, the C.I.A. prepared an analysis that all but pleaded with the White House to accept that the danger from Bin Laden was real.