It took America’s best-known evangelical pastor to get the presumed presidential candidates together before the election.

The results will be available for everyone to see live Saturday on national TV.

The Rev. Rick Warren of Saddleback Church in Southern California will talk to Sens. John McCain and Barack Obama about their convictions and the Constitution, leadership and poverty, personal faith and the U.S. role in the world.

“Two groups out there are worried about this,” said A. Larry Ross, a Warren spokesman. “There are the secularists who are afraid [Warren] is going to make this a Christian litmus test for the candidates. And there are the more conservative folks who are afraid he is going to wimp out and not ask the tough questions.”

Neither group’s fears will be realized, Ross said.

Warren’s questions will be wide ranging and tough, he promised. Warren’s church claims 22,000 members, and his book “The Purpose Driven Life” has sold tens of millions of copies.

The format will give the candidates about 50 minutes each, one at a time, Obama first. The candidates will be on stage together only briefly.

The fact that the forum is conducted by a minister says much about the respect Warren commands and the political landscape.

“I think it represents the fact that both [candidates] realize they need the Christian vote, and in particular evangelical votes, and Rick Warren represents a way of opening the door to that,” Os Guinness said.

Guinness is a well-known Christian writer and speaker. His book “The Case for Civility: and Why Our Future Depends on It,” calls for respectful dialogue and less of the nasty politics that characterize elections.

Evangelical voters accounted for 15 percent to 25 percent of the vote in the last presidential election, depending on whose definition of evangelical is used. They have been a solidly Republican block in recent years, but some polls such as those conducted by the Pew Forum on Religion & Public Life show their concerns are expanding beyond the hot-button issues of sexuality and abortion to causes such as world poverty, AIDS and the Darfur crisis. Warren has been a leader in expanding those concerns.

Burns Strider of the Eleison Group in Washington, who was Sen. Hillary Clinton’s campaign liaison to religious groups, said, “My sense is there are a lot of undecided voters from the faith community right now. In past cycles, they would have been sitting solidly in the Republican fold. But right now, they haven’t been totally sold by the Democrats … but they are certainly looking at their options.”

This forum will be more meaningful than past presidential debates because of the format and length of time each candidate will have to speak, Strider said.

But Guinness was sanguine about the potential results.

“I don’t expect it to play a very prominent part in the public debates,” he said.

The forum can be seen at 8 p.m. on CNN and Fox.