(CNN) -- The Rev. Rick Warren, often called America's most influential pastor, will be hosting Sens. Barack Obama and John McCain for what's being called the civil forum on the presidency.



Rick Warren will be hosting the civil forum on the presidency



Warren, who heads up the country's fourth largest church, is also an author whose books have sold more than 30 million copies.



The candidates will appear together at Warren's 20,000-member Saddleback mega-church in southern California where they each will be interviewed for an hour.



Warren spoke with John Roberts on CNN's American Morning about what he hopes to accomplish at the forum.



John Roberts: What do you want to hear from candidates Saturday night?



Rick Warren: You know, John, we're going to look at four different segments. One is a segment on leadership. What is the personal character, competence, and experience of each of these guys.



One section will be on what I call stewardship -- the role and responsibility of presidency, what they believe about the constitution, the role of America.



We're going to look at a section on world view -- all of the minefield questions that no matter how you answer them, somebody's not going to like it. Then we're going to look at America's role internationally. How we've been a blessed nation and how should we bless others.



Roberts: Are you going to ask them about issues like abortion and same-sex marriage? Pro-life advocates are hoping you do. There has been some criticism in some corners you have been soft-pedaling political issues that are central to evangelicals.



Warren: I think everybody will be surprised. I'm going to ask all of the tough questions. I just intend to ask them in a civil way. This is called a civil forum, which means you can disagree without demonizing the opposition. I think everybody wants to hear questions not just about those "moral issues," but also about a lot of other things, too. I'm trying to stake out a common ground for the common good.



Roberts: When you take a look at the evangelical vote in 2004, George Bush captured more than 75 percent of people who identify themselves as either born again or evangelical.



Our recent polling, CNN Opinion Research Corporation polls, found when it comes to John McCain, only 67 percent of evangelicals say they'll support him. Are you surprised at the shift?



Warren: It's interesting to me. Both of these men have been around for some time. Obama's written two books. Still a lot of people say, I'd like to know the real person. What are they really like? I'm hoping that'll happen in this forum.



Evangelicals have never been a monolithic voting base. Never. And the people who try to predict which way they're going to go in this election I think may be surprised after Election Day. You don't really know. I don't know, and I don't think anybody knows.



Roberts: As you know, John McCain in 2000 during the primaries ran afoul of evangelicals when he criticized Pat Robinson. He's tried to repair the relationship. Has he gone far enough?



Warren: The religious right, fundamentalists and evangelic evangelicals aren't synonyms for each other. I think John may have been talking about certain groups that he was worried about at that time. But he certainly rebuilt bridges among them today. It's just a question of whether they're going to vote on his issues or if they're going to vote on Obama's, and we'll see.



Roberts: As for you yourself in the most recent edition of Time magazine on which you're the cover, they've suggested you're evolving into the "superpolitical." Others have suggested you're becoming a spiritual entrepreneur. What do you make of the titles people are ascribing to you?



Warren: When you try to line out a middle ground -- common ground for the common good of America -- you get pot shots from both sides
What does the pastor plan to ask candidates? What kind of questions will be asked? Whose vote does Rick Warren say may surprise predictions? What kind of questions will be asked in a civil way? Who may be surprised? The forum won't just focus on what kind of issues? What is the pastor's name?
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