WASHINGTON — John Edwards sins “every day” and does not believe gay couples have a right to marry, while Senator Clinton says that although expressing her faith “doesn’t come naturally,” it sustained her through the turmoil of her husband’s infidelity.

Those were a few of the insights that came out of a presidential forum on faith and politics last night that explored the religious beliefs and practices of the three leading Democratic candidates. The contenders — Mr. Edwards, Mrs. Clinton, and Senator Obama of Illinois — each answered questions on a range of moral and religious topics, from gay rights and infidelity to the crisis in the Middle East.

For Mr. Obama, the event came hours after the Catholic League assailed his campaign for featuring on a faith outreach Web site testimonials from three pastors it deemed controversial.

At the forum, held at George Washington University and broadcast live on CNN, many of the questions were direct and personal, and some elicited unusual candor from the candidates, who were not on stage together.

Mr. Edwards, a former North Carolina senator who has run to the left of his rivals during the campaign, was asked if he thought gay couples had a right to get married. He had avoided giving a direct answer to a similar question at Sunday’s presidential debate. He said no, calling it a “personal belief.”

“I think there’s a difference between my belief system and what the responsibilities of the president of the United States are,” he said. “It is the reason we have a separation between church and state.”

In a lighter moment, Mr. Edwards said he couldn’t name the greatest sin he had committed in his life, but he conceded, “I sin every day.”

In what has been a rarity on the campaign trail, Mrs. Clinton faced a question about President Clinton’s extramarital affairs. Drawing murmurs from the crowd, CNN moderator Soledad O’Brien asked if her faith had helped her deal with her husband’s “infidelity.” In answering, Mrs. Clinton acknowledged that she was not as comfortable talking openly about her faith as others.

“I’m not sure I would have gotten through it without my faith,” she said. “I take my faith very seriously and very personally. I come from a tradition that is perhaps a little too suspicious of people who wear their faith on their sleeves. A lot of the talk about advertising about faith doesn’t come naturally to me.”

Like Mr. Edwards, Mrs. Clinton said she prayed often, although sometimes for “trivial or self-serving” things. “Sometimes I say, ‘Oh Lord, why can’t you help me lose weight,” she said to laughter from a crowd of more than 1,000.

The toughest question Mr. Obama faced was about the Middle East. He was asked whether Palestinian Arabs were being treated “morally and fairly and justly” by the Israelis.

“I think the Israelis want peace, and they want security,” Mr. Obama said. “Oftentimes in the midst of achieving security, there have been times when there’s no doubt that Palestinians have been placed in situations that we wouldn’t want our own families to be placed in.”

He added: “Israelis have been killed. They’ve got bombs flying into their territories right now. We would expect them to act appropriately to defend themselves.”

Mr. Obama was not asked about the criticism he faced earlier in the day from the president of the Catholic League, Bill Donohue, who singled out three pastors — the reverends Jeremiah Wright Jr. of Chicago, J. Alfred Smith Sr. of Oakland, and Michael Pfleger — that the Obama campaign featured on a Web site devoted to faith-based outreach. Mr. Donohue cited “racially inflammatory” statements by Mr. Wright, and he criticized Messrs. Smith and Pfleger for links to the Nation of Islam, a group he called “anti-Semitic, anti-Catholic, and anti-gay.”

“If these are the kinds of clergymen he admires, perhaps it’s best he shut down his new Web site and start all over again. It will take more than ‘God talk’ to get Obama out of this jam,” Mr. Donohue said.

Mr. Obama’s campaign issued a statement yesterday saying the senator is a “proud Christian” and that “while he may not agree with every element of every religion, he is open to others sharing their faith so that we can come together on what we have in common instead of focusing on our differences.” The statement did not specifically address Mr. Donohue’s charges or criticism.

Messrs. Wright and Pfleger did not respond to calls last night. In a brief message, Mr. Smith cited a positive relationship with the Jewish community, saying he “get[s] along well with everybody.”

Unlike the official debates, last night’s forum featured only the three candidates leading in fundraising and the polls, to the chagrin of second-tier candidates like Senator Dodd of Connecticut, Governor Richardson of New Mexico, and Senator Biden of Delaware. They were relegated to brief interviews on CNN afterward, along with Rep. Dennis Kucinich of Ohio. The campaigns of Messrs. Biden and Richardson each expressed dismay at the move.