The friendship was unusual from the start. Rick Warren was the conservative white pastor of a 20,000-member evangelical church in Orange County, Calif. Illinois Sen. Barack Obama was a liberal black politician and a rising star in the Democratic Party.

After meeting in Washington, D.C., in January, they started calling regularly. When Obama, a Punahou graduate, was writing his best-selling book, "The Audacity of Hope," he asked Warren, himself a best-selling author, to review the chapter on faith.

As Warren planned his second international conference on AIDS at his Saddleback Church, he asked Obama to address the group during a session titled "We Must Work Together."

Yesterday's session, despite disagreements over use of birth control, attempted bipartisanship when both Obama and a Republican senator took an AIDS test together, and he even garnered applause on several occasions.

Obama urged unity despite political differences to fight the disease that has killed 25 million people since the first case was reported in 1981. About 40 million are infected with HIV, the virus that causes AIDS.

"We are all sick because of AIDS," Obama said. "We are all challenged by this crisis."

Some evangelicals had criticized Warren for his different approach toward AIDS, which included working with gays. But the speech by the potential presidential contender has drawn renewed vitriol from conservative Christian radio hosts and pundits, as well as some evangelical preachers.

"Why would Warren marry the moral equivalency of his pulpit — a sacred piece of honor in evangelical traditions — to the inhumane, sick and sinister evil that Obama has worked for as a legislator?" wrote radio host and blogger Kevin McCullough.

Saddleback Church responded to the criticism with a statement earlier in the week defending Obama's appearance but also noting Warren's disapproval of some of his political beliefs.

"Let it be made very clear that Pastor Warren and Saddleback Church completely disagree with Obama's views on abortion and other positions he has taken, and have told him so in a public meeting on Capitol Hill," the statement read. "Our goal has been to put people together who normally won't even speak to each other. We do not expect all participants in the summit discussion to agree with all of our evangelical beliefs. However, the HIV/AIDS pandemic cannot be fought by evangelicals alone."

But the evangelicals' foray into AIDS work is relatively recent. According to religious scholars, they were among the loudest voices insisting AIDS was God's punishment for gays' behavior after the disease emerged in 1981. They remain slow to respond to the pandemic because of the disease's links to homosexuality and promiscuity, all prohibited by their interpretation of the Bible.

"This is a touchy subject for evangelicals," said John C. Green, a professor of religion and politics at the University of Akron and co-author of "Religion and the Culture Wars: Dispatches From the Front." The conference "really is a departure (but) you'll probably find a lot of the ambivalence really hasn't gone away."

Warren's wife, Kay, agrees that AIDS has been difficult to broach.

"Evangelicals have been really afraid," she said. "They don't want to talk about condoms. They don't want to talk about HIV because that means having to talk about sex. We want to break that kind of silence."

Kay Warren became aware of the vastness of the problem in 2002 after she read about the 12 million orphans the disease had left in Africa. This discovery spurred her to visit Mozambique, where she met an emaciated woman lying beneath a tree who was dying of AIDS. Warren grew angry that everyone, from the woman's family, to her church and government, had abandoned her. Then she realized she, her husband and their church in an affluent Orange County community were guilty of the same indifference.

"We had done nothing, we had done absolutely nothing," she said. "That hit me like a ton of bricks. Instead of being judgmental about what wasn't being done in other places, since we were doing nothing, we had to come back and repent. We have been so wrong. We haven't cared. We haven't said one word."

"I have no doubt if Jesus were walking the Earth today, he would be hanging out with people with AIDS," said Rick Warren, author of "The Purpose-Driven Life," the founder of Saddleback and among the nation's most influential evangelical preachers.

The Warrens believe that the vast network of houses of worship, acting with government, business and nonprofits, can provide medical treatment, nutrition and other services to people with AIDS. While they do not condone some of the behavior that might lead to the spread of AIDS, such as homosexuality and multiple sex partners, the Warrens said it is their sacred duty to show mercy to anyone the disease afflicts.

Alan Witchey, executive director of the AIDS Services Foundation of Orange County, didn't attend last year's conference because he had no interest in what the Warrens had to say. But his organization and the Warrens have had conversations in recent months, and Saddleback Church has conducted food drives for the foundation.

"Five years ago, if you had said to me, 'Would you ever sit down at a table with an evangelical group and talk about how to collaboratively provide services?' I would have thought that couldn't happen. It just would have been beyond my imagining of the world," he said.

The Associated Press contributed AIDS conference information for this report.