In making the case for war against Iraq, Vice President Cheney has continued to suggest that an Iraqi intelligence agent met with a Sept. 11, 2001, hijacker five months before the attacks, even as the story was falling apart under scrutiny by the FBI, CIA and the foreign government that first made the allegation.

The alleged meeting in Prague between hijacker Mohamed Atta and Iraqi Ahmed Khalil Ibrahim Samir al-Ani was the single thread the administration has pointed to that might tie Iraq to the attacks. But as the Czech government distanced itself from its initial assertion and American investigators determined Atta was probably in the United States at the time of the meeting, other administration officials dropped the incident from their public statements about Iraq.

Not Cheney, who was the administration's most vociferous advocate for going to war with Iraq. He brought up the connection between Atta and al-Ani again two weeks ago in an appearance on NBC's "Meet the Press" in which he also suggested links between Iraq and the Sept. 11 attacks.

Cheney described Iraq as "the geographic base of the terrorists who have had us under assault for many years, but most especially on 9/11." Neither the CIA nor the congressional joint inquiry that investigated the assault on the World Trade Center and the Pentagon found any evidence linking Iraq to the hijackers or the attacks. President Bush corrected Cheney's statement several days later.

Cheney's staff also waged a campaign to include the allegation in Secretary of State Colin L. Powell's speech to the United Nations in February in which he made the administration's case for war against Iraq. Cheney's chief of staff, I. Lewis "Scooter" Libby, pressed Powell's speechwriters to include the Atta claim and other suspected links between Iraq and terrorism, according to senior and mid-level administration officials involved in crafting the speech.

When State Department and CIA officials complained about Libby's proposed language and suggested cutting large sections, Cheney's associates fought back. "Every piece offered . . . they fought tooth and nail to keep it in," said one official involved in putting together the speech.

The vice president's role in keeping the alleged meeting in Prague before the public eye is an illustration of the administration's handling of intelligence reports in the run-up to the war, when senior officials sometimes seized on reports that bolstered the case against Iraq despite contradictory evidence provided by the U.S. intelligence community.

Cheney's office declined to comment. Mary Matalin, a former senior aide to Cheney who still provides the vice president with advice, said Cheney's job is to focus on "the big picture." His appearance on "Meet the Press" on Sept. 14, she said, was intended to "remind people that Iraq is part of a bigger war that will require patience and sacrifice."

Cheney does not fully vet his speeches or public statements with the CIA or the wider intelligence community for accuracy, according to several administration officials, but usually gives the CIA a list of possible points or facts that might be used in a speech or appearance.

Matalin said Cheney "doesn't base his opinion on one piece of data," but has access to information that cannot be declassified because it would harm national security or compromise sources. "His job is to connect the dots in a way to prevent the worst possible case from happening," she said, but in public "he has to tiptoe through landmines of what's sayable and not sayable."

The claim that Atta, an Egyptian and Sept. 11 hijacker, had met with al-Ani in early April 2001 has been a constant element of the vice president's case against Iraq. Surveillance cameras at the Radio Free Europe building in Prague had picked up al-Ani, an intelligence officer at the Iraq embassy, surveying the building in April, five months before the Sept. 11 attacks. The tape was made available to Czech intelligence. Al-Ani was expelled at the U.S. government's request soon afterward for conduct incompatible with his diplomatic status.

In October 2001, after pictures of Atta had circulated publicly, an Arab student who worked as an informant for BIS, the Czech Security Information Service, told the service he had seen Atta meeting with al-Ani in April.

That November, Stanislav Gross, the Czech Republic's interior minister, said publicly that al-Ani and Atta had met in Prague. A short while later, Czech Prime Minister Milos Zeman told Powell that the two had discussed targeting the Radio Free Europe building, not the Sept. 11 targets.

On Dec. 9, 2001, Cheney said on "Meet The Press" that "it's been pretty well confirmed that he did go to Prague and he did meet with a senior official of the Iraqi intelligence service in Czechoslovakia last April, several months before the attack."

But that same month, Czech President Vaclav Havel was retreating from the more definitive accounts provided by his government, saying there was "a 70 percent" chance the meeting took place. Indeed, while Czech officials never officially backed away from their initial stance, officials at various agencies say that, privately, the Czechs have discredited the accuracy of the untested informant who came to them with the information. According to one report, Havel quietly informed the White House in 2002 there was no evidence to confirm the meeting.

The Czechs had reviewed records using Atta's name and his seven known aliases provided by the CIA and found nothing to confirm the April 2001 trip. Meanwhile, CIA and FBI officials were running down thousands of leads on Atta and the other 18 hijackers involved in the Sept. 11 plot.

U.S. records showed Atta living in Virginia Beach in April 2001, and they could find no indication he had left Virginia or traveled outside the United States.

Even so, on March 24, 2002, Cheney again told NBC, "We discovered . . . the allegation that one of the lead hijackers, Mohamed Atta, had, in fact, met with Iraqi intelligence in Prague."

A few weeks later, in April, FBI Director Robert S. Mueller III told a San Francisco audience, "We ran down literally hundreds of thousands of leads and checked every record we could get our hands on, from flight reservations to car rentals to bank accounts." The FBI, he said, could find no evidence that Atta left or returned to the United States at the time.

In May, senior FBI and CIA analysts, having scoured thousands of travel records, concluded "there was no evidence Atta left or returned to the U.S.," according to officials at the time.

But on Sept. 8, 2002, Cheney, again on "Meet the Press," said that Atta "did apparently travel to Prague. . . . We have reporting that places him in Prague with a senior Iraqi intelligence officer a few months before the attacks on the World Trade Center."

"What does the CIA say about that?" asked host Tim Russert. "Is it credible?"

"It's credible," Cheney replied. "But, you know, I think the way to put it would be it's unconfirmed at this point."

As war loomed closer, the Atta allegation generally began to disappear from the administration's public case against Iraq. Bush did not mention Atta or the Prague meeting in his Jan. 28 State of the Union address, when he sought to show Iraq's links to terrorism.

But behind the scenes, the Atta meeting remained tantalizing to Cheney and his staff. Libby -- along with deputy national security adviser Stephen J. Hadley, a longtime Cheney associate -- began pushing to include the Atta claim in Powell's appearance before the U.N. Security Council a week after the State of the Union speech. Powell's presentation was aimed at convincing the world of Iraq's ties to terrorists and its pursuit of chemical, biological and nuclear weapons.

On Jan. 25, with a stack of notebooks at his side, color-coded with the sources for the information, Libby laid out the potential case against Iraq to a packed White House situation room. "We read [their proposal to include Atta] and some of us said, 'Wow! Here we go again,' " said one official who helped draft the speech. "You write it. You take it out, and then it comes back again."

Libby described the material as a "Chinese menu," simply the broadest range of options, according to several administration officials. "The papers were designed to assist [Powell's] preparation by organizing a lot of materials so that he could choose the order and evidence he found most compelling, although some of it, in the end, could not be declassified," said one administration official.

But other officials present said they felt that Libby's presentation was over the top, that the wording was too aggressive and most of the material could not be used in a public forum. Much of it, in fact, unraveled when closely examined by intelligence analysts from other agencies and, in the end, was largely discarded.

"After one day of hearing screams about who put this together and what are the sources, we essentially threw it out," one official present said.

Cheney's staff did not entirely give up. Late into the night before Powell's presentation, Libby called Powell's staff, waiting at the United Nations in New York, to question why certain material was not being included in the terrorism section, according to two State Department officials.

Earlier this month, on his most recent "Meet the Press" appearance, Cheney once again used Atta to subtly suggest a connection between Iraq and Sept. 11, 2001.

"With respect to 9/11, of course, we've had the story . . . the Czechs alleged that Mohamed Atta, the lead attacker, met in Prague with a senior Iraqi intelligence official five months before the attack, but we've never been able to develop anymore of that yet, either in terms of confirming it or discrediting it."

Defense and intelligence officials say al-Ani, who was apprehended by U.S. forces earlier this year, has denied meeting with Atta.

Research editor Margot Williams contributed to this report.

Minutes after the Sept. 11, 2001, attack, Vice President Cheney was in the operations center with his chief of staff, I. Lewis Libby, far right, national security adviser Condoleezza Rice, center left, and his wife, Lynne Cheney, far left. Lead hijacker Mohamed Atta met with an Iraqi agent in Prague, Vice President Cheney maintains, despite evidence to the contrary.