Obama's complaints about former President Bill Clinton's attacks on him on behalf of his wife's campaign boiled over at a rancorous debate. Hillary Clinton flayed Obama for his praise of the late President Ronald Reagan, a Republican icon reviled by many Democrats.

The back-and-forth was so fierce that former North Carolina Sen. John Edwards, running a distant third in the Democratic race, accused them of squabbling and often had trouble getting a word in edgewise.

The Republican presidential contenders, meanwhile, flooded Florida ahead of a crucial showdown on January 29 in a nomination race where three different candidates have scored wins and a fourth, Rudy Giuliani, is looking for a breakthrough.

For Democrats, South Carolina is the next battleground in a seesawing race to find a candidate for the election in November. Obama, an Illinois senator, holds a slim lead in polls in the state, where more than half of the likely voters on Saturday will be black.

In the televised debate, Clinton accused Obama of praising ideas from the opposition party over the past 10-15 years after Obama said last week that Reagan "changed the trajectory of America."

"Now I personally think they had ideas. But they were bad ideas," said Clinton, a New York senator who would be America's first woman president. "They were bad ideas for America."

Obama, who would be the first black U.S. president, shot back that he was in no way praising Republican ideas, but simply saying that Reagan had been able to bring political rivals together.

When Clinton interrupted to say she had not mentioned Reagan, Obama said, "Your husband did."

"I'm here, he's not," she tossed back.

"Well I can't tell who I'm running against sometimes," Obama replied, a sign of his increasing exasperation at the attack role Bill Clinton is playing in her campaign.

U.S. economic woes provided an important background in the debate, in which all three participants expressed fears of a recession and denounced President George W. Bush's $145 billion stimulus plan as too little, too late.

But the personal exchanges were remarkably sharp even for a Democratic campaign that has been rough and tumble.

Obama said while American jobs were being shipped overseas years ago, Clinton had been serving as a corporate lawyer "sitting on the board of Wal-Mart," a company that many see as responsible for selling cheap imported products that have resulted in many U.S. jobs going overseas.

"SLUM LANDLORD IN INNER CITY CHICAGO"

Clinton angrily accused Obama of practicing law and representing a political contributor, Tony Rezko, "in his slum landlord business in inner city Chicago." Prosecutors have accused Rezko of fraud and Obama's campaign has given to charity campaign contributions from donors linked to Rezko.

At times CNN host Wolf Blitzer had trouble maintaining control of the debate, which took place on a national holiday to honour King, the slain civil rights leader.

Clinton and Obama came into South Carolina with tempers on edge after a bruising fight over Nevada on Saturday, won by Clinton.

Edwards is desperate for a good showing in South Carolina, his birth state. He raised questions about dozens of votes Obama made when he was an Illinois state senator when he simply voted "present" instead of yes or no.

"Why would you vote over 100 times present?" Edwards asked.

Neither party has established a clear front-runner in the race to pick the two candidates to contest the November 4 presidential election as the first major state-by-state battles produced multiple winners.

In Miami, Republican candidate John McCain wooed Cuban-American voters, an influential bloc of Republican voters, telling them he would not lift the trade embargo on communist Cuba until it holds free elections.

McCain is in a tight race in Florida with former Massachusetts Gov. Mitt Romney, former New York Mayor Giuliani and former Arkansas Gov. Mike Huckabee.

McCain, an Arizona senator, won last Saturday's Republican primary in South Carolina and earlier in New Hampshire, while Romney won Nevada on Saturday and Michigan a week ago.

Giuliani sat out the early voting states to concentrate on Florida in hopes it will give him momentum heading into "Super Tuesday" on February 5, when 22 states hold their contests.