Tony Blair has insisted the Iraq war was justified despite his acceptance that no weapons of mass destruction were present.
Blair: Fallible, but Iraq war justified
Mr Blair disputed the UN secretary general Kofi Annan's claim the war was illegal, saying it was justified on the basis of broken UN resolutions.
He had done what any "reasonable" prime minister would have done, he argued.
But Conservative leader Michael Howard has for the first time directly accused Mr Blair of lying.
Mr Howard told the New Statesman: "I think people hold the view pretty firmly now that they were lied to over Iraq.
"I don't think that's the only thing they were lied to about... but Iraq is the great catalyst for the loss of trust in the government."
After a day of behind the scenes talks, Labour delegates will go ahead as planned with a vote on calls to set an early date for pulling British troops out of Iraq.
Supporters of the critical motion are predicting it will be defeated as they claim the big unions are set to vote against it but Labour officials say there have been no negotiations over timetable for withdrawal.
The conference will also vote on a statement from Labour's National Executive Committee which refers to the UN resolution talking about the mandate for the multi-national force in Iraq ending in December 2005.
Mr Blair earlier told BBC Radio 4's Today that states had to be "active" not "reactive" after the 11 September attacks.
He did not accept that Saddam Hussein was "not a threat" although "it never was the case" that he was about to launch an attack on the US or Britain.
Mr Annan recently said the Iraq war was not legal because Britain and the US had failed to secure a second UN resolution authorising military action.
"That is his view - it is not our view," Mr Blair said.
"The view we took at the time and we take it now is that the war was justified legally because he [Saddam Hussein] remained in breach of UN resolutions."
Asked about his partial apology in his speech to Labour's conference on Tuesday, he said: "I can apologise for the information that we gave that has turned out subsequently to be wrong - although I maintain very strongly it was given in good faith and shared by other people.
"But the trouble is I cannot apologise for getting rid of Saddam Hussein or [say] the basis that we went to war was wrong."
It was vital the international community took a "totally new approach" after 11 September to stop weapons of mass destruction falling into the hands of terrorists, he said.
Mr Blair dismissed suggestions he had accepted the intelligence on Iraqi weapons programmes because he had already decided to take military action.
"There was no doubt in respect of the intelligence about Saddam and weapons of mass destruction," he countered.
"The intelligence that we had was intelligence that I believe any sensible or reasonable prime minister would have said there is a clear WMD threat here."
The action in Iraq had led to Libya winding up its weapons programme, and meant there was a "better chance of getting Iran and North Korea into compliance than we have ever had", he said.
He was "as fallible as anybody else ... in the end all you can do as prime minister is say this why I have taken this judgement," he said.
But he "passionately" believed that the terrorist threat would "engulf" us if it was not dealt with.
His comments come as the fate of British hostage in Iraq Ken Bigley remains uncertain and follows the death of two more UK soldiers in the southern Iraqi city of Basra.
Mr Blair rejected suggestions the public would not trust him if he were to propose military action in similar circumstances again.
But he acknowledged: "In the light of what has happened, people will want to know that any evidence that is given is very soundly based."
He said he was aware the decisions he had taken on Iraq had not made him very popular.
But he added: "The time to trust politicians most is actually when they are courting popularity least because... they are doing something they believe in."
Mr Milburn's promotion has been seen as a snub to Gordon Brown
Liberal Democrat party president Simon Hughes said: "Nobody in the free world wanted Saddam Hussein to continue, there wasn't any disagreement about that - everybody wanted him out of the way.
"The problem was how to justify regime change in international law."
A spokesman for the UK Independence Party said Tony Blair had "created Britain's Vietnam".
He said: "What other errors in his foreign policy are we yet to hear about? How can we trust him to portray Britain's interests on the world stage or even a European one?"