Prime Minister Blair and President Bush said their farewells at the White House yesterday. It was an emotional moment for both leaders. Their seven-year trans-Atlantic partnership has, in its way, been as important for the defense of the Free World as that of Prime Minister Churchill and President Franklin Roosevelt, or Prime Minister Thatcher and President Reagan.

This time, the main threat has come from enemies who wage war against Jews and Christians in the name of Islam. So it is significant that the president and prime minister are united by the bond of a shared faith. They have been partners not only in war and peace, but also in prayer. Both are among the most devout statesmen ever to lead their countries.

Whereas Mr. Bush has talked openly about being born again, Mr. Blair has generally kept his religious experiences to himself. But that public reticence has not been able to quell periodic speculation about his private beliefs. His spokesman once told an inquisitive journalist: “We don’t do God.” Yet over his 10 years in office, evidence has accumulated that Mr. Blair would like to leave the Church of England, the faith of his parents, in order to convert to Catholicism, the faith of his wife and the one in which they have raised their four children.

While Mr. Blair was fêted in Washington, back home his impending conversion was the talk of London. A priest who is a close family friend was reported in the Times as saying that the prime minister would declare himself a Catholic soon after he leaves Downing Street on June 27.

Father Michael Seed, who has converted several prominent politicians at Westminster, often celebrates Mass for the Blair family at Downing Street. His relationship with the Blair family is partly based on a common concern for the down-and-outs who gather outside Westminster Cathedral to be fed in a Catholic charity that is London’s largest center for the homeless, the Passage. Cherie Blair, a highly successful attorney who is a product of the same working-class Liverpool as the Beatles, has encouraged her children to help out in the soup kitchens there.

However, Father Michael is not only charitable but also convivial, and it was in conversation with friends after a recent memorial service that he let slip the prime minister’s most closely guarded secret. He now says he does not know if Mr. Blair will be formally received into the church but that he believes that the prime minister’s commitment goes far beyond that of a dutiful spouse in a mixed marriage. “He’s been going to Mass every Sunday,” Father Michael said. “He goes on his own when he is abroad, not just when he is with his wife and children.” If Mr. Blair were to convert, however, he would be the first Catholic prime minister since the Reformation. Though he will have left office before being publicly received into the church, friends say he has been a Catholic in all but name for many years. The Blairs have attended private Mass both with the last pope, John Paul II, and the present one, Benedict XVI, and Mr. Blair is believed to have received communion from both pontiffs.

Why is Mr. Blair abandoning the Church of England? The answer is probably that, like many Anglicans, he feels as if his native church has abandoned him. A church that is obsessed with the ordination of homosexuals or women has nothing to say on the confrontation of Islam and the West. It has been unable to provide the moral compass essential to a man who aspires to lead his country in a time of war — and a religious war at that.

Mr. Blair sees his political career as a vocation, and he has often spoken of the voice of conscience that guides him in the solitude of command. He says God will judge whether he was right to go to war in Iraq — and he seems comfortable with that prospect. This is a leader who abominates what the pope calls the “dictatorship of relativism” and who feels a strong affinity with the Catholic Church’s refusal to allow itself to be evicted from the public square.

So it was logical for Mr. Blair, having decided to retire from politics, to seek a new vocation in setting up a foundation dedicated to reconciliation among the three faiths that trace their descent from Abraham: Judaism, Christianity, and Islam. Details of the Blair foundation have not yet been made public, but it is safe to assume that he won’t favor the kind of ecumenism that glosses over moral and theological conflicts.

Mr. Blair will try to build bridges to those brave and isolated figures in the Muslim world who publicly denounce the Islamist attempt to reverse 1,000 years of Judeo-Christian civilization. And he will have no truck with the Christians and Jews who blame Israel for the hatred and violence unleashed by terrorists against America and Europe.

Tony Blair’s spiritual journey has taken him through some dark valleys before finding its final destination in the church of not only popes and cardinals but Mother Teresa. His profession of faith should not be the occasion of Catholic triumphalism, but of quiet satisfaction that one of the greatest leaders of our time has also proved to be a man of magnanimity and humility.