Blair, whose trust ratings have plunged since the overthrow of former Iraqi leader Saddam Hussein, conceded his decision to join the war had hurt, angered and disappointed many of his supporters.

"Iraq has divided the international community. It has divided the party, the country, families, friends," he told delegates at the annual Labor Party conference.

"I know many people profoundly believe the action we took was wrong," Blair said. "I ask just one thing: attack my decision but at least understand why I took it and why I would take the same decision again."

Blair faces the most testing period of his six-year rule. Doubts over his case for war have been fueled by the failure to find any weapons of mass destruction in Iraq -- Britain's main justification for military action.

A judicial inquiry into the suicide of a weapons expert who questioned parts of Britain's dossier on Iraqi weapons has further undermined the prime minister.

Blair said letters he received from parents of British soldiers who died in Iraq -- both supportive and critical -- offered him plenty to reflect on.

"Don't believe anyone who tells you when they receive letters like that they don't suffer any doubt."

But he insisted the danger from weapons of mass destruction represented the "security threat of the twenty-first century."

"There was no easy choice. So whatever we each of us thought, let us agree on this: We who started the war must finish the peace."

Weekend opinion polls gave Labor its worst ratings since Blair became party leader in 1994 and swept to two successive landslide election victories.

One poll published on Sunday showed 41 percent of Labor members also want Blair to resign before the next election.

But Blair signaled no retreat on policies which have upset many on the left-wing of his party. "I can only go one way. I've not got a reverse gear," he said.