Blair again accepted that British intelligence pointing to stockpiles of chemical and biological weapons was flawed, but he insisted he had been right to back the U.S.-led invasion.
"I take full responsibility and apologize for any information given in good faith that has subsequently turned out to be wrong," Blair told the House of Commons, in a stormy session dominated by the war.
"What I do not in any way accept is that there was any deception of anyone. I will not apologize for removing Saddam Hussein. I will not apologize for the conflict. I believe it was right then, is right now and essential for the wider security of that region and world."
Eighteen months after the war began, Iraq still haunts Blair and dominates the political debate in Britain.
He appears to be weathering the storm, however. Although Blair's popularity slumped in the wake of the invasion, according to recent opinion polls it has stabilized and he is considered more trustworthy than his main political opponents.
Blair's principal reason for joining the U.S.-led offensive was his belief that Saddam had stockpiles of weapons of mass destruction. The government highlighted the danger in a September 2002 dossier as it tried to persuade a skeptical public of the need for war.
But anconcluded in July that British intelligence on Iraqi WMD was flawed, that the government had pushed its case to the limits of available intelligence, and it had left out vital caveats in the dossier.
Four inquiries have cleared Blair's government of deliberately misleading the public about the Iraqi threat, but that has failed to satisfy his political opponents. The row over weapons led to a bitter dispute between Downing Street and the British Broadcasting Corporation, and contributed to the suicide of.
Opposition Conservative Party leader Michael Howard pointed out on Wednesday that before the war, Blair said that intelligence had "established beyond doubt" that Saddam had continued to produce chemical and biological weapons, when evidence was patchy at best.
"I support the war. It was the right thing to do," said Howard. "But will you realize that before you can move on, there is one matter that you must deal with. You didn't accurately report the intelligence you received to the country. Will you now say sorry for that?"
Blair hotly contested any suggestion he misled the country.
"I cannot bring myself to say that I misrepresented the evidence, since I do not accept that I did," he countered.
Blair accused Howard of "playing politics" over Iraq. Like U.S. Democratic presidential nominee John Kerry, Howard supported the war and his subsequent attacks have opened him to charges of "flip-flopping" on the issue.
"Having supported the war, having urged us to go to war, (he) is now trying to capitalize on anti-war sentiment to try to give himself credibility," Blair said, to loud cheers of support from his own Labor Party lawmakers.
The Iraq Survey Group last week concluded thaton the eve of the invasion. The government was further embarrassed Tuesday when it acknowledged that spy masters had now formally withdrawn a claim that Saddam could launch chemical and biological weapons on 45 minutes' notice. The claim had featured prominently in the government's dossier.
After a review of intelligence, the spy agency MI6 had ruled the source of the claim, an Iraqi military officer in western Iraq, was unreliable. MI6 had been directed to the source by the Iraqi National Accord, an opposition group linked with Iraq's interim Prime Minister Ayad Allawi.
Blair's support for the war has strained unity within his own party, as at least two anti-war Cabinet members have abandoned him and dozens of members have voted against the prime minister on test votes. Iraq strained an already tenuous relationship between Blair, a moderate reformer, and the left wing of the formerly socialist Labor party.
But given Blair's unprecedented success as the man who led Labor to victories in 1997 and 2001, his rivals within the party are unlikely to abandon him heading into elections expected next spring.
Yet the war could hamper Blair's efforts to create a lasting legacy as the prime minister who revamped Britain's public services and brought the historically isolated United Kingdom into closer contact with continental Europe. Referenda on joining the euro and accepting the new European Union constitution are expected in coming years.