At the 56th annual National Prayer Breakfast on Thursday at the Washington Hilton, a bevy of lawmakers, religious leaders and foreign heads of state will listen to a keynote speaker whose name hasn’t yet been officially revealed. But sources confirm that former British Prime Minister Tony Blair will speak.

Such heavyweights as Mother Teresa, a Catholic, and Jordan’s King Abdullah II, a Muslim, have spoken in previous years. Blair, who famously converted to Roman Catholicism in 2007, established the Tony Blair Faith Foundation last year to “to promote respect and understanding about the world’s major religions and show how faith is a powerful force for good in the modern world,” according to the group’s Web site.

President Barack Obama, who attended the breakfast as a Senator, will briefly address the gathering, and several Members will participate with prayers and Scripture readings.

Interest in this year’s breakfast is high, particularly among foreign guests because “they haven’t met President Obama yet,” said Rep. Vernon Ehlers (R-Mich.), who is co-chairing this year’s breakfast with Rep. Heath Shuler (D-N.C.).

Each Member of Congress was allowed two tickets to make available for purchase by their constituents, and Obama received a supply of tickets to offer to his own guests. The ballroom and overflow space could hold nearly 3,500 guests, according to the Hilton.

The week leading up to the breakfast is filled with groups meeting for regional meals, fellowship and prayer. Black said he makes himself available to pray with groups of visitors in a suite at the Hilton for four to five hours on Tuesday, Wednesday and Thursday. He said people who come to pray with him have a wide variety of concerns relating to national, international and personal issues, and they often stay in touch long after the breakfast.

Black also offers a prayer with the participants of the program before the breakfast begins. He said each year’s speaker is the “critical factor in the distinctive nature of the prayer breakfast.”

For example, Black said, in 2006 “Bono brought awareness of how religion can divide more than unite, and he talked about growing up in Ireland, where if you were Catholic, that meant you many times would be fighting Protestants, and vice versa.”

Former Kansas Sen. Frank Carlson (R), a regular at Senate prayer meetings, coordinated the first breakfast in 1953 — Dwight Eisenhower was president, and evangelist Billy Graham was among the attendees. The event’s name changed from the Presidential Prayer Breakfast to the National Prayer Breakfast in 1970.

The breakfast has provoked controversy among groups who see it as a break in the barrier between church and state. Ehlers thinks that criticism doesn’t hold water.

“If you read the Constitution, it’s very clear that the government has no right to say anything about voluntary associations like this,” he said, adding that no one is forced to attend and no federal funds are used for the gathering.

The other criticism of the breakfast is that it doesn’t represent all faiths equally, a task Ehlers notes can be pretty difficult. However, a Cherokee Indian chief will offer the opening prayer Thursday, Ehlers said. Ehlers is a member of the Christian Reformed Church in North America, while Shuler is Southern Baptist.

The Fellowship Foundation, the organizer responsible for the breakfast and for regular prayer meetings of Members on Capitol Hill, is Christian.

This year’s event will be broadcast live online at eventbuilder.com.