Barack Obama and Hillary Rodham Clinton insisted this week that the Democratic nominating contest should turn on issues such as health care and energy. But despite their stated hopes, a different subject keeps pushing itself into the campaign: The role of race.

In the latest sign of a racial rift, two prominent black pastors warned Wednesday that if Hillary is the nominee, black voters could become so discouraged by the campaign that they might stay home in November.

“This is a virtual race war, politically,” said the Rev. Eugene Rivers of the Azusa Christian Community, a Pentecostal church in Boston.

Rivers, one of the country’s leading Pentecostal ministers, said black voters were especially offended by Hillary’s suggestion this week that Obama could join her on the ticket as her running mate. “Blacks aren’t going to sit back while the winning candidate is told to sit at the back of the bus,” he said, adding that the Democratic Party and Hillary risk handing the election to the presumptive Republican nominee, John McCain.

Bishop Charles Blake of Los Angeles, who as leader of the 6 million-member Church of God in Christ presides over one of the nation’s largest Christian denominations, said that black voters could come to feel so disheartened that “their whole motivation for participating in the political process in this election would be greatly reduced.”

The pastors’ comments came during a week in which racial issues have retaken a central role. Obama’s 24-point victory Tuesday in the Mississippi primary highlighted the party’s racial rift, with Obama, who is black, winning 90 percent of black voters and Hillary, who is white, winning 70 percent of white voters.

On Wednesday, a high-profile Hillary supporter, former Democratic vice presidential nominee Geraldine Ferraro, stepped down from the campaign after making comments against Obama that some considered racially divisive.

“We ought to keep this on the issues,” she said Tuesday to The Associated Press. “There are differences between us. There are differences between our approaches on health care, on energy, on our experience, on our results that we’ve produced for people.”

Obama said Wednesday that discussions of race and gender were counterproductive.

“I don’t think identity politics has served the Democratic Party well,” he said. “I think it’s been an enormous distraction — I think that when we are in these conversations it means that people are not recognizing their common concerns around health care, their common interests in getting decent jobs, their common interests in making sure that we’re not loading up the national debt for the next generation to pay.”

But the candidates acknowledged that a campaign pitting the would-be first female president against the would-be first black president was destined to touch delicate nerves in a party built in part on coalitions of blacks and women.

Obama complained Wednesday that at times Hillary has invoked race in subtle ways.

“I do think that the Hillary campaign has talked more during the course of the last few months about what groups are supporting her and what groups are supporting me, and trying to make the case that the reason she should be the nominee is there are a set of voters that Obama might not get,” he said. “That seems to track certain racial demographics. And I disagree with that.”

he overwhelmingly won the heavily black South Carolina primary in January.

The finger-pointing has gone both ways. Hillary in January cited an Obama campaign document to show that her rival was encouraging the media to focus on race — forcing Obama to blame the strategy on “overzealous” staffers. And some members of the Congressional Black Caucus who are backing Hillary — and who are under pressure to switch their loyalties — have complained that Obama supporters are targeting them because of their race.

One prominent lawmaker who switched to Obama’s side after coming under that pressure was Rep. John Lewis of Georgia, a veteran of the civil-rights movement.

One of the black Hillary backers in Congress, Rep. Emanuel Cleaver of Missouri, said in a recent interview that he feared a “backlash” if whites see blacks pressuring each other to vote based on race.