The religious souls of US presidential hopefuls Barack Obama and John McCain go under scrutiny Saturday when the two field questions from one of the country's most famous evangelical preachers, AFP reported.
At a pivotal moment of their increasingly nasty presidential race, the Democratic and Republican rivals are due to take part in "A Civil Forum on the Presidency" at the huge Saddleback Church of charismatic preacher Rick Warren - a rare move in a White House race where forums and debates are usually mediated by prominent media figures.
"What I'm trying to do is stake out what I call the common ground for the common good," Warren told Fox News on Friday.
"I think there are a lot of Americans who are disaffected by both the left and the right, whether it's the secular left or the religious left or whether it's the secular right or religious right."
Warren, who has sold millions of copies of his book "The Purpose Driven Life" and is a prominent HIV/AIDS activist and missionary, leads a congregation of more than 20,000 in the Lake Forest, California megachurch, and has sought to bridge the divide between conservative evangelicals and more liberal Americans.
"This is a critical time for our nation and the American people deserve to hear both candidates speak from the heart - without interruption - in a civil and thoughtful format absent the partisan 'gotcha' questions that typically produce heat instead of light," Warren said earlier in a statement.
As their White House battle grows rougher, the two senators will appear at the church Saturday together for the first time since they effectively secured their party nominations.
But that will only come after being quizzed separately by Warren.
Obama is due to field an hour of questions first, and McCain then gets his turn, but without having first heard how his Democratic rival answered.
Only then will the two meet together on stage.
The forum, which is expected to get blanket cable news coverage and be streamed live on the Internet, will serve to underline the prominent role of religious faith in the US political scene.
McCain will be looking to forge links with the powerful "religious right" movement of conservative evangelicals with whom he has endured a testy relationship.
Obama is confident in talking about his Christian faith - more so than many other Democratic politicians - though has been dogged by inaccurate, Internet-spread rumors that he is a closet Muslim.
The forum heralds a crucial period in the presidential race, with both candidates expected to soon name their vice presidential running mates, ahead of their party nominating conventions, the Democrats on August 25- 28 in Denver, Colorado, and the Republicans on September 1- 4 in Minneapolis-Saint Paul, Minnesota.
While their comments on moral principles and personal spirituality Saturday will be closely parsed, the stumbling US economy remains at the center of the fight between Obama and McCain.
"The economy is the one issue that continues as the dominant voter concern," said Michael Dimock, associate director of research at the Pew Research Center.
McCain will be coming into the forum with more than a week on the campaign trail alone behind him, as Obama has been relaxing with his family on holiday in his native Hawaii.
Their campaigns have meanwhile been building up their war chests for the ten weeks before the November 4 election.
McCain set the stage Friday for an advertising blitz against Obama by raking in a monthly fundraising record of 27 million dollars in July, aides said.
His total was however dwarfed by Obama's monthly fundraising figure, which was released Saturday and showed 51 million dollars piled up in July.
Obama is also celebrating after recruiting the two millionth donor to his campaign, evidence of an unprecedented grass roots movement that his team hopes will help carry him to victory in November.