By John Blake, CNN

(CNN) - After the Rev. Martin Luther King Jr. first gained wide public recognition in the mid-1950s, he made a special request to evangelist Billy Graham.

King was poised to join Graham on one of his barnstorming crusades, but he would do so only on one condition. He asked Graham to publicly speak out against segregation, a request Graham declined, says San Diego State University historian Edward Blum.

“What Graham feared was losing all of his influence,” Blum says. “For him, personal salvation was primary, justice secondary. For King, justice was primary.”

After President Obama this week became the first sitting president to endorse same-sex marriage, black clergy and churchgoers could be facing a question that's similar to the one that fractured King and Graham: Should my ideas about personal holiness trump my notion of justice?

The answer to that question is evolving – just as Obama’s views on gay marriage have been. Poll numbers and interviews with black clergy suggest it’s simplistic to say that the black church is anti-gay marriage and may desert Obama, as some pundits have suggested.

Equal rights for some people?

Some black pastors take the approach of Graham, who recently came out in support of a successful drive to amend North Carolina’s constitution to ban same-sex marriage and domestic partnerships.

For them, personal salvation is primary; homosexuality a sin, and so is gay marriage. Their enthusiasm for Obama will be diminished, Blum says.

“It will be, ‘I’m going to vote for him, but I’m not going to talk about him much,’ ” Blum says. “It’s the difference between voting for him, or voting for him and putting out a street sign and making sure your neighbor gets to the poll.”

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Others in the black church say their approach centers on justice.

The Rev. Joseph Lowery, who was a part of King’s inner circle, says Obama had to support gay marriage because he believes in equal rights.

“You can’t believe in equal rights for some people and yet not believe in equal rights for everybody,” Lowery says. “That includes the right to marry the person of your choice. Equal rights for some people are an oxymoron.”

Lowery says Obama’s announcement was “more revolutionary” than the moment that President Lyndon Johnson went on national television during the heyday of the civil rights movement and called for racial equality, declaring, “We shall overcome.”

Obama’s “We Shall Overcome” moment will force Americans – black and white – to reexamine positions on same-sex marriage, Lowery says.

“A lot of white people didn’t believe in desegregation until the Supreme Court declared it unconstitutional,” says Lowery, who presided over Obama’s inauguration. “And then they began to rethink it and basically came to the same conclusion.”

Pastor or president?

At least one black minister in North Carolina captures another neglected dimension to the debate. He opposes same-sex marriage but doesn’t like the energy Christians devote to opposing it.

“He’s the president of the Untied States, not the pastor of the United States,” says the Rev. Fred Robinson, who lives in Charlotte. “America is a democracy, not a theocracy. I’m not going to vote on one issue.”

Robinson says some Christians are better at being against something than for something. Christian divorce rates are just as high as those for secular marriages, he says.

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“Our witness is stronger if we actually show that we believe in marriage and lived in and honored it,” he says. “That would be a greater witness than running to the polls to enshrine discrimination in the state constitution.”

The Rev. Tim McDonald, founder of the African-American Ministers Leadership Council, says he opposes same-sex marriage, but he is more concerned about issues like health care, education and jobs.

He's interested to see how black pastors handle Obama’s announcement when they step onto the pulpit Sunday.

“I don’t see how you cannot talk about it,” he says. “I have to. You can say I’m opposed to it [same-sex marriage], but that doesn’t mean I’m against the president.”

McDonald says more black pastors are talking about same-sex marriage than ever before: “Three years ago, there was not even a conversation about this issue – there wasn’t even an entertainment of a conversation about this.”

Polls show that black opinions on same-sex marriage are changing.

According to a Pew Research Center poll conducted in April, 49% of black respondents described themselves as opposed to marriage between gays and lesbians, 14% fewer than in 2008. The percentage of African-Americans in favor of it increased from 26% in 2008 to 39% in 2012.

In 2008, Californians voted on Proposition 8, a measure that would make same-sex marriage illegal in the state, at the same time that they cast ballots for president.

CNN exit polling showed that 70% of California African-Americans supported Prop 8 but that the overwhelming majority - 94% - also backed President Obama.

Black pastors who preach in favor of same-sex marriage know they may pay a price if they take Obama’s position, says Bishop Carlton Pearson.

Pearson is a black minister who says he lost his church building and about 6,000 members when he began preaching that gays and lesbians were accepted by God.

“That’s the risk that people take,” he told CNN. “A lot of preachers actually don’t have a theological issue. It’s a business decision. They can’t afford to lose their parishioners and their parsonages and salaries.”

Pearson navigates the tension between the Bible’s call for holiness and justice this way:

“I take the Bible seriously, just not literally,” he says. “It’s more important what Jesus said about God than what the church says about Jesus.”

CNN staff writer Stephanie Siek contributed to this report.