London -- Prime Minister Tony Blair, who upended the old politics of liberalism and conservatism in Britain and pushed for an "ethical" foreign policy, said yesterday that he will step down June 27 after more than a decade in power.
Blair, 54, one of Britain's longest-serving prime ministers, resurrected the Labor Party from the electoral backwaters in 1997 on a wave of national optimism, only to see it founder over an unpopular war in Iraq.
His successor almost certainly will be Gordon Brown, the introverted, intellectual chancellor of the exchequer who worked side by side with him to create the doctrine of New Labor but fell out with Blair in recent years over when he would be allowed to have his own day in the sun as prime minister.
"Sometimes the only way you conquer the pull of power is to set it down," said Blair in his long-awaited announcement speech, which was part bittersweet and part defiant.
Addressing a roomful of Labor Party members, Blair sought to underline achievements that have brought near-record prosperity to Britain and injected new life into health and education services, even as he quietly but defiantly defended his decision to send British troops to war in Iraq.
"I ask you to accept one thing. Hand on heart, I did what I thought was right," Blair told the supporters, who alternately cheered and wiped back tears, in his home constituency in the northeast England district of Sedgefield.
Blair called up the image of the Sept. 11 attacks, and the decision he made, which was to prove the most fateful of his premiership, to "stand shoulder to shoulder with our oldest ally," the United States.
"And so Afghanistan and then Iraq, the latter bitterly controversial, and removing Saddam and his sons from power," he said. "The blowback since from global terrorism and those elements that support it has been fierce and unrelenting and costly, and for many it simply isn't and can't be worth it.
"For me, I think we must see it through," he said. "The terrorists who threaten us here and round the world will never give up if we give up. It is a test of will and of belief, and we can't fail it."
The pressing question surrounding Brown is what he will do about Iraq. There are few clues in what he has said, though some of his allies hint at changes of emphasis.
He has discouraged expectations of change in Britain's approach to Iraq if, as expected, he takes over as Labor Party leader and prime minister.
"There will be no sense in which we seek to walk away from decisions we made," he said in an interview last month with Time magazine, speaking about Iraq.
For his part, President Bush expressed confidence yesterday that Brown would continue to support the war.
Only days before his announcement, Blair concluded 10 years of patient diplomacy and oversaw the induction of a new power-sharing government in Northern Ireland - a settlement he attributed in part to a new, more prosperous, more tolerant Britain "at home in its own skin."
"I don't think Northern Ireland would have been changed unless Britain had changed," he said.
Blair's long-awaited announcement came at a time when the Labor Party has seen its membership drop by half since the first of his three general election victories in 1997.
By this month, Labor's credibility had sunk to the point that the party took just 27 percent of the vote in elections for local councils in England and the parliaments in Scotland and Wales - losing Scotland by one seat to the Scottish National Party. Labor Parliament members had seen the trouble coming, and had pushed Blair as early as last fall to set a timetable for his departure, which some have labeled "the long goodbye."
Deep uncertainty within the party and negotiations over Cabinet reshuffling that are sure to characterize Blair's remaining weeks at Downing Street prompted Conservative Leader David Cameron this week to urge a rapid transition.
"This is the government of the living dead," he declared. "Why do we have to put up with even more paralysis?"
But a lengthy farewell full of last-minute policy legacies on fighting terrorism, renewing Britain's nuclear arsenal and ending the conflict in Northern Ireland is an essential precedent for a politician seen as the consummate communicator - surely one of the few world leaders with his own YouTube site and podcasts featuring his conversations on history, climate change, his "passion for science" and aid to Africa.
That Blair saw the World Trade Center attacks as a global turning point, which created an obligation on the part of like-minded nations to act, was apparent in the immediate aftermath. Blair's remarks after the American attack were widely regarded as more forceful and eloquent than those of President Bush.
More than that, Blair showed he shared Bush's belief that democratic values could be used as agents of change against repressive regimes and ancient hostilities.
Even before the Sept. 11 attacks and the subsequent transport system bombings that killed 52 in London in 2005, Blair had fashioned his doctrine of an "ethical foreign policy" that would give "new momentum" to arms control, work for a ban on landmines, and forge a commitment to push the environment and human rights up on the international agenda.
Blair made the international case for intervening in Kosovo in 1999 and again in Sierra Leone in 2000 in an effort to use British troops as shields against escalating violence.
"Tony is your classic liberal interventionist," said Clive Solely, former chairman of the parliamentary Labor Party. "Before we were in power, Bosnia happened, and we didn't intervene, and he saw how, incidentally, that's when some of these extreme Islamic groups got their start. Sierra Leone was a great success. Then comes Iraq. It did go appallingly wrong, but I don't think his motivation is any different.
"His frustration is that things like the U.N. are unable to deal with your tyrannical regimes, or failing state regimes, because there isn't a structure for enforcement," Solely continued. "His belief is if the United States and Europe do things together, they can sort the world out."
Blair has seen himself as a "bridge" between the U.S. and Europe, but has made it clear that America, with its status as the world's leading power, was Britain's most important ally - even if that meant jeopardizing relations with European neighbors, many of whom opposed the war in Iraq.
As it happened, Blair's first foreign secretary, Robin Cook, resigned in protest when Britain joined the invasion of Iraq in 2003 without broad international support. And other aspects of the "ethical" dimension in foreign policy began to crumble when the British government was accused of dissembling over evidence of weapons of mass destruction in Iraq.
Kim Murphy writes for the Los Angeles Times. The Associated Press contributed to this article.