No British prime minister has ever staked his reputation on his relationship with America to such an extent as Tony Blair, who announced yesterday that he is standing down after 10 years.

It was typical of the man to put his decision to “stand shoulder to shoulder with our oldest ally” after September 11, 2001, at the heart of his farewell speech. He will tender his resignation to the queen on June 27.

Mr. Blair knows that his decade in office will be judged in the light of his loyalty to America, but he rejected the accusation that he has been “slavish.” In politics, as in economics and culture, he proclaimed: “Britain is not a follower today. Britain is a leader.”

Addressing the British people in the uniquely personal way that he first made his own when he led the mourning for Princess Diana, Mr. Blair offered his thanks but also his apologies “for the times when I’ve fallen short.”

This was not, however, an apology for Iraq. Mr. Blair’s conscience is clear. He defended what he acknowledged was the “bitterly controversial” decision to go to war. He conceded that, though Saddam Hussein and the Taliban had been overthrown quickly, the “blowback” proved to be “fierce, unrelenting, costly.” Some thought the war “wasn’t worth it.”

But Mr. Blair insisted that Iraq could not be abandoned until we have “seen it through” to ultimate victory: “The terrorists will never give up if we give up.”

What evidently irks Mr. Blair more than anything is the suggestion that he deliberately and cynically sent British soldiers to die on the strength of a lie.

“Hand on heart, I did what I thought was right,” he declared. “I ask you to accept one thing. I may have been wrong. That’s your call,” he told his skeptical countrymen. But then he repeated: “I did what I thought was right for our country.”

It was a deeply emotional speech, which in some quarters will be taken as final proof that Mr. Blair is now more American than British. I did not read it that way at all.

His peroration was an expression of the deepest, most genuine patriotism. “This country is a blessed nation,” he said. “This is the greatest nation on earth.”

Churchill would have understood. If it is unfashionable to take pride in one’s country, then Mr. Blair is unfashionable.

He answered those critics who accuse him of “messianic zeal” by reminding them of the loneliness of leadership: “Your duty as prime minister is to act according to your conviction. … Your ultimate obligation is to decide.”

As the scene of his announcement, he had chosen not the elegant surroundings of 10 Downing St. but the warm embrace of his constituents in Sedgefield, the northeastern town in County Durham that he has represented throughout his quarter-century in politics.

Having led the Labor Party to three election victories, there was the usual defense of his record. But the speech was a conciliatory one. He admitted that the great expectations with which he was elected in 1997 were “not fulfilled in every part,” but added: “I would not have wanted it any other way.”

Mr. Blair declared himself an incorrigible optimist: “I leave office with high hopes” for a nation that, he said, has “rediscovered itself” over the past 10 years.

This was the speech of a man who has certainly discovered himself since “the completely unexpected” occurred on September 11. “Politics may be the art of the possible,” he said, “but at least in life, give the impossible a go.”

For anyone else, this would have been an impossible speech. Nobody else could have written it. Nobody else could have delivered it with such panache. Nobody else but Mr. Blair would have meant every word of it. A great prime minister should bow out with a great speech — and he did.