The evidence "did not meet the standards we use for the president," said Condoleezza Rice, the national security adviser and the minder of Mr. Bush's pronouncements. That is putting it politely. American intelligence agencies questioned the accuracy of the British report, and even doubted their own evidence.

Now Ms. Rice and her colleagues are pointing the finger at George J. Tenet, the director of central intelligence, who never read the draft of the State of the Union speech that the White House sent him and, by his own admission, never asked that it be withdrawn.

It is a curious defense, one that acknowledges that the president cited dubious intelligence and admits that the vetting process failed, while arguing that history may yet prove him right. It plays to the central argument that Mr. Bush and his aides have used in trying to quiet a growing political storm: that Mr. Hussein posed an urgent threat, no matter what was going on in the uranium mines of Niger.

But if the White House's changing — and sometimes contradictory — time line of events leading up to the speech is to be believed, Ms. Rice's aides knew as early as October that some underlying evidence was suspect. The C.I.A., according to that time line, changed its assessment of the reliability of that evidence three times in four months — enough to make clear that there was reason to doubt the quality of the evidence.

That has led to questions that Mr. Bush and his aides have still not answered. Why did Mr. Bush's aides keep coming back to the Africa case as "an emblematic example" of Mr. Hussein's surreptitious activities, as one administration official terms it, if so many in the intelligence world were questioning it?

Further, how did it survive so many drafts of the State of the Union speech in January, only to be thrown out, days later, by Secretary of State Colin L. Powell, who found the evidence so thin that he dared not take it to the United Nations for his own presentation?

By the time Mr. Powell made it to the C.I.A. to prepare his own case against Iraq — three nights after the State of the Union address — the intelligence agencies were "not carrying it as a credible item," he said in an interview. How it met Mr. Bush's standards and not Mr. Powell's is one of the mysteries the White House has not addressed.

The answer, some in the intelligence world say, is that the evidence did not change — but the political environment around it did.

When the first reports of Mr. Hussein's reported interest in Niger flowed in, apparently from a foreign intelligence service, they caught the eye of aides to Vice President Dick Cheney, perhaps the most hawkish corner of a hawkish administration, but also one with long experience in Iraq. They knew that Mr. Hussein had obtained uranium ore — called yellowcake — in the African country two decades ago. It seemed reasonable he might go back for more. The request for further investigation went back to the C.I.A.

The report came back that Niger denied it had sold anything. But Ari Fleischer, who spent his last day as White House press secretary defending the administration's decision-making, noted today that it included an account of Iraqi businessmen who met with Niger officials seeking to "expand business contacts." As one official on White House national security staff said the other day, "Their contacts in Niger didn't think that meant they wanted to open a McDonald's. They interpreted it to mean they wanted more uranium."

But there was no proof, and an eager speechwriter included the specifics in a speech Mr. Bush was scheduled to give in Cincinnati on Oct. 7 that Iraq had sought 550 metric tons of yellowcake. Mr. Tenet called Stephen J. Hadley, the deputy national security adviser, to have the dubious statement deleted. It was.

It is what happened next that has investigators searching for evidence that intelligence was manipulated for political purposes. Three weeks after the speech, the evidence that Mr. Tenet removed showed up in the classified "National Intelligence Estimate," which was sent to Congress. So was the statement that Iraq was looking for uranium in Somalia and Congo. There was a vague footnote explaining that the State Department had doubts. It turns out that so did many in the C.I.A., who say the charge never should have been in the formal intelligence estimate, a document reflecting the views of many intelligence agencies. 

Its appearance in print cleared the way for repetition of the tale. And someone — the White House won't say who — put the reference into early drafts of the State of the Union address.

Mr. Fleischer insisted that the new reference "was different" from the one removed in Cincinnati — it was a general claim that Mr. Hussein had "sought" uranium in Africa, not that he had obtained any. But clearly someone in the White House wanted more details to come out of the president's mouth. A mid-level N.S.C. official called the C.I.A. for more details.

After all, specifics would add dramatic effect and underscore the urgency to act. Chemical and biological weapons are hard to deliver and harder to understand, but the world knows the mushroom cloud, the image Ms. Rice used in describing what the next Sept. 11 attack could look like if Mr. Hussein gave nuclear weapons to terrorists.

According to the accounts provided by the White House, the C.I.A. official, Alan Foley, pushed back, saying the specifics could not be verified. That is when the White House reached for the unclassified British report, and attributed the statement to Prime Minister Tony Blair's intelligence services. "It would have been better not to include it," Donald H. Rumsfeld, the secretary of defense, said on television on Sunday, when asked why his boss was citing foreign intelligence reports instead of his own.

That seemed to state the safely obvious. But was the report cited to manipulate the evidence?

"A lot of bull," Mr. Fleischer said about that accusation today, with the candor of a man about to go to the private sector. Inside the C.I.A. and the State Department, though, many are still asking how a White House aware of the doubts could have shown such caution in October, and thrown it to the winds in January.