A heated brawl over the role of race in the primary elections between the two leading Democratic presidential hopefuls, Senators Clinton and Obama, will ensure that the sensitive subject the party tries hard to ignore will dominate tomorrow’s candidates’ debate in Nevada.

Surrogates from both camps have been waging an increasingly heated battle over the allegiance of black voters, with each accusing the other of introducing racism into the closely fought contest. Yesterday, the issue boiled over, with the competing senators making charge and counter-charge over who was responsible for raising a topic generally considered too treacherous to address.

Mrs. Clinton returned to a remark she made last week, contrasting her experience with Mr. Obama’s persuasive oratory, in which she said Martin Luther King’s eloquence needed President Johnson’s Washington savvy before civil rights legislation could be enacted.

Calling Dr. King “one of the people I admire most in the world,” Mrs. Clinton repeated her claim that it was Johnson’s mastery of Congress as much as Dr. King’s rhetoric that led to change. “Dr. King didn’t just give speeches. He marched, he organized, he protested, he was gassed, he was beaten, he was jailed,” she said on NBC’s “Meet the Press.”

“He understood that he had to move the political process and bring in those who were in political power. He campaigned for political leaders, including Lyndon Johnson, because he wanted somebody in the White House who would act on what he had devoted his life to achieving.”

She bemoaned the fact that her views on Dr. King had been misinterpreted, causing her to draw fire from Rep. James Clyburn, one of America’s top black congressmen, and Donna Brazile, who ran Vice President Gore’s presidential bid and successfully lobbied to have Dr. King’s birthday declared a federal holiday.

“This is an unfortunate story line the Obama campaign has pushed very successfully,” Mrs. Clinton said. “Clearly, we know from media reports that the Obama campaign is deliberately distorting this.”

Shortly afterward, Mr. Obama denied to reporters that he had sanctioned the garbling of Mrs. Clinton’s remarks. “The notion that this is somehow our doing is ludicrous,” he said,

Notwithstanding his denial, however, he could not resist taking a shot at his main rival. “Senator Clinton made an unfortunate remark, an ill advised remark, about Dr. King and Lyndon Johnson. … She, I think, offended some folks who felt that it somehow diminished King’s role in bringing about the Civil Rights Act,” he said.

“She started this campaign saying that she wanted to make history, and lately she’s been spending a lot of time rewriting it,” he said. Mr. Obama continued the attack, dismissing Mrs. Clinton’s experience in government as a hindrance to achieving change. “What we saw this morning was why the American people are tired of Washington politicians and the games they play,” he said.

The war of words over race may emerge as the issue that decides the eventual victor in the Democratic race. After the Nevada caucuses on Saturday, all eyes will turn to the January 26 primary in South Carolina, where a third of the population is black.

Speaking to the African-American Northminster Presbyterian Church congregation in Columbia, S.C., yesterday, Mrs. Clinton was careful to praise Mr. Obama. Claiming that to be a woman running for president was the result of the wider civil rights movement, she said, “I am so proud of my party, I am so proud of my country, and I am so proud of Senator Barack Obama. … I am standing here, Senator Obama stands before you, as a result of the generations of men and women who protested and picketed. … We are all in this struggle together.”

Mr. Obama set out on his presidential campaign ignoring his ethnicity in the hope that he would reach well beyond African Americans for support. In the Iowa caucuses, where voters had to declare their allegiance in front of others, his color appeared not to be an issue.

However, the reluctance of white voters to vote for a black candidate in a secret primary ballot has been cited by some pollsters as a reason for Mr. Obama’s surprise defeat in New Hampshire.

While Mrs. Clinton’s appeal to minority voters might be diminished if the accusations of disrespecting black heroes were to stick, the introduction of race into the wider debate may benefit her campaign. If even registered Democrats cannot keep the issue of race out of their primary race, it is argued, Mr. Obama’s ethnicity is sure to become an issue — and a liability — in the presidential election in November.

Mr. Obama’s tactics came under fire yesterday from one of Mrs. Clinton’s most prominent black woman supporters, Rep. Sheila Jackson Lee, a Democrat of Texas. “You cannot transcend race and then use race as an issue,” she told CNN.