The presumed Democratic and Republican nominees are slated for back-to-back appearances at a California faith forum described as a "conversation, not a confrontation."

They will be interviewed separately on such topics as the presidency and Constitution, the role of the United States in the world, global poverty, leadership and compassion by the Rev. Rick Warren, pastor of the 22,000-member Saddleback Church in Orange County, Calif.

Spokesman Larry Ross said Warren also will ask each candidate about his faith because "personal faith is your worldview and that determines how you will lead."

Evangelicals make up about 20 to 25 percent of the electorate, USA Today says.