An official inquiry reported Wednesday that key portions of British intelligence claiming that Iraq had weapons of mass destruction were "seriously flawed" and "open to doubt," but it found no evidence that Prime Minister Tony Blair's government had deliberately distorted the evidence or misled the public in making the case for war.

The inquiry's report was particularly critical of an intelligence dossier the government published in September 2002, saying it omitted important caveats and gave the impression that the information it was based on was "fuller and firmer" than it actually was.

Wednesday's report singled out the dramatic claim -- repeated four times in the dossier -- that Iraq could launch chemical or biological weapons within 45 minutes of an order, saying the dossier had failed to make clear that the claim was "vague and ambiguous." MI6, Britain's secret intelligence service, now has doubts about the validity of the claim, the report noted.

Overall, the 196-page document painted a portrait of intelligence services under pressure to come up with data supporting the case for war from sources that were sparse, limited and, in the end, often unreliable.

But the report, issued by a special five-person panel chaired by former cabinet secretary Robin Butler, stopped well short of the strong criticism leveled by the Senate intelligence committee against U.S. spy agencies last week. It specifically stated that John Scarlett, who chaired the committee that issued the 2002 dossier, should be allowed to take up his new post as the head of MI6 next month.

Asked to specify who was to blame for mistakes in the dossier, Butler said at a news conference: "It was a weakness on the part of all those who were involved in putting together the dossier. I think that they collectively have to take the responsibility for that."

A visibly relieved and buoyant Blair told the House of Commons that he fully accepted the report's findings and recommendations and took responsibility for any errors the government had made. But Blair, saying that "I have searched my conscience," said he still believed that the Iraqi people and the world were better off without Saddam Hussein, despite the fact that weapons of mass destruction had not been found.

Opposition lawmakers said the House of Commons would not have approved the decision to go to war in March 2003 had members known how thin the intelligence was. "It's not a question of responsibility, it's a question of credibility," said Michael Howard, leader of the opposition Conservative Party, which had withdrawn its participation in the Butler inquiry because it considered the panel's mandate too restrictive.

The report said the government's decision in the spring and summer of 2002 to move toward confronting Iraq was based not on new intelligence about a potential threat, but rather grew out of Blair's belief that Iraq was a danger that needed to be dealt with and a desire to stay in alignment with the Bush administration.

"There was no recent intelligence that would itself have given rise to a conclusion that Iraq was of more immediate concern than the activities of some other countries," the inquiry said.

It cited a secret government paper in March 2002 that advised that "regime change" had no basis in international law and that there was no recent evidence of Iraqi complicity in terrorism. Officials were left with the argument that Iraq had failed to comply with U.N. resolutions on ending its weapons programs. But the 2002 paper had warned that proof of noncompliance "would need to be incontrovertible and of large-scale activity. Current intelligence is insufficiently robust to meet this criterion."

Nonetheless, the inquiry said, Blair pressed the case for confrontation and ordered the Joint Intelligence Committee, a cabinet-level group that includes the heads of Britain's three main intelligence services, to produce a dossier to support his position.

The inquiry said new intelligence arrived in four reports from three confidential sources in August and September 2002, but each of the reports assumed that Iraq had chemical and biological weapons rather than providing evidence of it. Two-thirds of the committee's human intelligence on Iraq came from one source, according to the report. "We were struck by the relative thinness of the intelligence base," the inquiry said.

Accounts by agents in Iraq were particularly unreliable because Hussein's government was extremely secretive and because MI6's evaluation procedures were weak, the inquiry said. Agents were asked to report on issues well beyond their usual expertise, and because of the scarcity of sources, "more credence was given to untried agents than would normally be the case," it stated.

After the war ended and MI6 sent analysts to Iraq to track down and confirm the material it had relied upon, the report said, doubts -- "and in some cases serious doubts" -- emerged about the reliability of at least three sources whose intelligence had helped to underpin British assessments.

Although the Joint Intelligence Committee's confidential assessments to Blair before the war emphasized that sources were thin and questionable, the dossier prepared for the public omitted those caveats. "Warnings were lost about the limited intelligence base on which some aspects of these assessments were being made," the panel concluded. This was "a serious weakness."

When new intelligence from an untested source arrived in September, two weeks before the dossier was published, MI6 used it in the dossier but refused to share it with weapons experts at the Defense Ministry's intelligence service who might have cast doubts on its validity, the inquiry said. That intelligence was withdrawn in July 2003 because it was found to be unreliable.

With publication of the dossier in the name of the Joint Intelligence Committee, the inquiry concluded, "more weight was placed on the intelligence than it could bear."

But the report defended as "well founded" the dossier's claim that Iraq had sought to obtain enriched uranium from African countries. The CIA has questioned the claim, saying it was based on forged papers, but the Butler panel said there were other sources for the assertion.

The inquiry expressed surprise that British policymakers and analysts did not reevaluate their findings in early 2003 after U.N. inspectors failed to find weapons in Iraq.

The inquiry also criticized Blair's leadership style. Although there were 24 separate discussions of the war in Blair's cabinet, the inquiry said, ministers were given no warning of most of the sessions or given copies of the detailed papers that some departments had prepared. Instead, most of the discussions were held on the basis of oral presentations, "reducing the scope for informed collective political judgment."

Blair has been President Bush's strongest international ally on Iraq, a stance that has seriously damaged his popularity with voters here. He said Wednesday that he hoped the new report -- the fourth inquiry to have focused on the war and cleared the government of falsifying or exaggerating intelligence -- would finally convince critics that he had acted in good faith.

"No one lied, no one made up intelligence, no one inserted things into the dossier against the advice of the intelligence services," he told lawmakers.

But Robin Cook, a former cabinet minister who resigned to protest the war, said that "the unavoidable conclusion" of the report's content is "that we committed British troops to action on the basis of false intelligence, overheated analysis and unreliable sources."

Inquiry chairman Robin Butler holds a copy of the report.Blair in House of Commons.