WASHINGTON -- Despite deep doubts by the CIA and FBI, the White House is now backing claims that Sept. 11 skyjacker Mohamed Atta secretly met five months earlier with an Iraqi agent in the Czech capital, a possible indication that President Saddam Hussein's regime was involved in the terrorist attacks.

In an interview, a senior Bush administration official said that available evidence of the long-disputed meeting in Prague "holds up." The official added, "We're going to talk more about this case."

Hard evidence that Hussein was involved in the Sept. 11 attacks would give strong ammunition to the administration in its efforts to build domestic and international support for a military campaign to topple the Iraqi leader.

But the CIA and FBI concluded months ago that they had no hard evidence to confirm Czech claims that the Prague meeting took place.

A federal law enforcement official said Thursday, however, that the FBI has been reviewing Atta's possible ties to Iraq, including travel and phone records, with "renewed vigor" in recent weeks. He said he didn't know whether any clear connections had now been found, but he called the case one of the "more urgent" priorities for the bureau.

A U.S. intelligence official said Thursday that the CIA remains "open to the possibility" of Iraqi sponsorship of the attacks but that no hard evidence or intelligence has emerged to prove it. "There is nothing hard," the official said.

The White House previously has declined to publicly back those who insist that the alleged Prague meeting shows Iraq's hand in last fall's attacks. The purported meeting with Atta, the apparent leader of the hijackers, is the only allegation that has come to light suggesting a direct tie between Hussein and Sept. 11.

But the administration faces growing pressure to provide a more-convincing rationale for a potential military campaign against Iraq or a covert operation to topple or kill Hussein.

A growing number of Democratic and Republican members of Congress, though largely supportive of a possible overthrow of the Iraqi leader, have begun questioning the risks and costs of such a military effort and its aftermath. So have key U.S. allies in Europe and the Middle East. If the administration can build a strong case against Iraq, analysts say, those questions and doubts are likely to vanish.

Until now, the administration has largely argued that military action against Iraq is justified because of the danger that Hussein's regime is secretly building nuclear, chemical or biological weapons that could be used against the United States or its allies.

In the interview, the senior Bush administration official acknowledged that the White House needs to expand its effort to persuade its allies and the American public that Hussein poses an immediate danger.

"In our discussions with our friends around the world, I cannot remember a single one who has not said, 'Of course, the world would be better off without this man in power.' There are those who are concerned about how to do it, and the consequences," said the official, who spoke on condition of anonymity.

"We would be the first to say that we need to talk more about this," the official added. "But when the case is clear, people will understand in even greater detail why regime change is necessary."

The official said Hussein poses several threats to U.S. interests. The Iraqi leader is a "tactical threat," the U.S. official said, because his Iraqi forces fire on U.S. and British military pilots patrolling swaths of northern and southern Iraq under mandates set by the United Nations.

Hussein is also "spreading terror" in the Middle East, by methods that include offering to pay $25,000 to the families of Palestinian suicide bombers in Israel and the occupied territories, the official said.

"He also has links to international terrorism," the official said. "There is growing evidence that that includes organizations like Al Qaeda. That would be a mortal threat to the United States."

Asked for specifics, the official cited Atta's alleged meeting in Prague. "The evidence that was out there holds up," the official said.

On Tuesday, Defense Secretary Donald H. Rumsfeld told a news conference that Iraq had "a relationship" with the Al Qaeda terrorist network, but he declined to be more specific.

"I mean, we're not on the ground" in Iraq, he said. "But are there Al Qaeda in Iraq? Yes. Are there Al Qaeda in Iran? Yes. Are there Al Qaeda in the United States? Yes."

Reports of the meeting first emerged last October when Czech Interior Minister Stanislav Gross announced that Atta had flown to Prague in April 2001 and met with Ahmad Khalil Ibrahim Samir Ani, a vice consul at the Iraqi Embassy.

Ani, thought to be an officer in Iraq's intelligence service, was expelled from the Czech Republic on April 22, 2001, after surveillance cameras caught him studying the downtown building that houses America's Radio Free Europe, which has an Iraqi-language service that broadcasts anti-Hussein programs.

After the Sept. 11 attacks, an informant for the Czech counterintelligence service told officials that he recognized Atta's photo in the newspaper and that Atta had met months earlier with Ani. Czech officials have stood by that account.

However, no tapes or photos of the visit have surfaced, and U.S. officials said an exhaustive review failed to find any proof that he had traveled to Prague in April 2001. Records indicate that he was in Virginia Beach, Va., between April 8 and 11, 2001—when he was reported to be in Prague—possibly casing U.S. Navy facilities.

"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," FBI Director Robert S. Mueller III said in a little-noticed speech in April that publicly outlined the extent of the investigation into Atta's movements and its results.

In March, CIA Director George J. Tenet told a Senate committee that it would be a mistake to dismiss Hussein as a possible sponsor of the attacks.

Tenet said that although Hussein and Osama bin Laden had clear religious and ideological differences, they had "mutual antipathy" toward the U.S. and Saudi Arabia and that "tactical cooperation between them is possible."

But since Tenet's testimony, the CIA has found "no known support by Saddam for Al Qaeda cells," according to a U.S. intelligence official who spoke on condition of anonymity.

The official said that evidence showed Atta had "passed through" Prague in 1999 and 2000. He said it was possible that Atta had traveled to Prague again from the U.S. in spring 2001.

The official added that no new evidence substantiates the Prague meeting and that the CIA had not been asked to reevaluate the case. The official said the agency has not found evidence to support allegations that Bin Laden or his top lieutenants traveled to Baghdad.

President Bush has given indications all year that he intends to oust Hussein, but critics say Bush has not made a detailed case about the risks and costs of such a venture. The debate continues to be shaped by news leaks.

In Congress, hard questions have come both from Democratic lawmakers and from such Republicans as Sens. Charles Hagel of Nebraska, John McCain of Arizona and Richard G. Lugar of Indiana, who is the acting ranking minority member of the Senate Foreign Relations Committee.

The committee, chaired by Sen. Joseph R. Biden Jr. (D-Del.), opened two days of hearings Wednesday that will continue in September and are likely to build pressure on the White House to explain its case.

"We must estimate soberly the human and economic cost of war plans and postwar plans," said Lugar, who is also urging the White House to seek a congressional vote before military action.

Norman Ornstein, an expert on Congress at the American Enterprise Institute think tank, said that last winter lawmakers were largely unquestioning about a possible war, and Bush could have gotten 70% to 80% congressional approval for military action in a vote.

"Now there's substantially more skepticism and pointed questioning," Ornstein said.

Germany and France are urging caution in any military effort. French President Jacques Chirac said this week that the two European countries would back a military effort only if it was mandated by the U.N. Security Council.

Some analysts have predicted that the administration would try to bolster its public case by discussing what they believe is an Al Qaeda-Iraq link.

"I think they're going to pull all that together," said Gary J. Schmitt, a conservative strategist and executive director of Project for a New American Century, a think tank.

He said he expected the administration to argue that Hussein should be ousted because of the alleged Al Qaeda link as well as the threat that the regime may pose by development of weapons of mass destruction.

Schmitt said he believed the Al Qaeda link would have the widest appeal, but he added that he hoped the White House does not give it more emphasis than the latter argument, which he considered more compelling.

Times staff writer Josh Meyer in Washington contributed to this report.