LAKE FOREST, Calif. — Barack Obama and John McCain briefly shared a stage at Orange County's cavernous Saddleback Church yesterday as they discussed what their faith means to them and highlighted their vastly different views on issues, none more stark than abortion.

Obama said that it was "above my pay grade" when asked to define when a baby gets human rights. But McCain quickly answered, "At the moment of conception." And he promised: "This presidency will have pro-life policies. That is my commitment."

After McCain's brief response and sustained applause, Rick Warren, the church's pastor, quipped: "OK. We don't have to go longer on that one."

Obama offered an extended explanation of his views, adding that he believes there is a "moral and ethical dimension" to abortion. He pledged to work to reduce the number of abortions and provide resources to allow women to decide to keep their babies.

The two major-party candidates talked with Warren in back-to-back, hourlong interviews at the Lake Forest mega-church before about 2,800 people, discussing abortion, faith, same-sex marriage, stem-cell research and a series of major public policy issues.

Between the interviews, Obama greeted McCain with a brief handshake and hug.

Campaign aides to both candidates said the forum was a rare chance for both men to talk about their faith and to use Warren's network to reach out to evangelicals and other Christians.

The appearance of the two candidates at the church was somewhat unusual. But Obama forged a relationship with Warren in 2006 after meeting in Washington; Obama even asked Warren to review a chapter on faith in his book "The Audacity of Hope."

Warren's weekly services draw about 22,000 and his book, "The Purpose Driven Life," became an enormous best-seller.

The forum highlighted the stylistic differences between the two candidates. Warren's first question — which three people each candidate relied on — showed that contrast.

Obama, the Democratic candidate, named his wife and grandmother, before moving on to a list of past and current senators, including conservative Oklahoma Sen. Tom Coburn.

McCain crisply named Gen. David H. Petraeus, the top U.S. commander in Iraq; John Lewis, the Georgia congressman and civil rights leader; and his economic adviser, Meg Whitman, the former CEO of eBay.

Polls show McCain holds a sizable lead over Obama among evangelicals. A late July poll by CNN/Opinion Research Corp. found that 67 percent of white evangelical voters favor McCain; 24 percent support Obama.

Warren asked both candidates about America's greatest moral failure.

Obama said it was "that we still don't abide by that basic precept of Matthew that whatever you do for the least of my brothers, you do for me." Saying that this applied to poverty, racism and sexism, he continued, "There's a pervasive sense, I think, that this country, as wealthy and powerful as we are, still don't spend enough time thinking about the least of us."

McCain said it was that America has not done enough to serve a cause greater than its self-interest.

His own greatest moral failure, Obama said, was his use of drugs and alcohol as a youth. "When I find myself taking the wrong step, I find that a lot of the time it is because I am trying to protect myself and not do God's work," he said.

McCain said it was the failure of his first marriage.

Asked about a position that they held 10 years ago that they have since changed their views on, Obama mentioned his initial concerns that welfare reform could have "disastrous results." "It worked better than a lot of people anticipated," he said.

McCain, raising an issue that he has pressed on the campaign trail as a response to high oil prices, said he had abandoned his opposition to offshore oil drilling. "We've got to drill now. We've got to drill here," he said.

Both were asked about their most gut-wrenching decisions.

McCain said it was his decision not to accept an offer to be released early as a prisoner of war in Vietnam. He said it was "the toughest I've ever made."

Obama cited his opposition to the war in Iraq, saying that he agonized about it. "There is a solemn obligation (to soldiers being sent to war) that you do everything you can to get that decision right," he said.

Both said they opposed same-sex marriage.