"Barack Obama easily won South Carolina's bitterly contested Democratic presidential primary with the aid of heavy black support on Tuesday, dealing a setback to rival Hillary Clinton after a week of political brawling.

Obama, an Illinois senator who would be the first black U.S. president, beat Clinton and John Edwards handily in the latest fight in a back-and-forth Democratic nominating battle. Clinton and Edwards were running close for second place, according to exit polls.

South Carolina was the latest test for Obama and Clinton, a New York senator, in their escalating battle for the right to represent the Democratic Party in November's presidential election.

After two consecutive losses, in New Hampshire and Nevada, Obama badly needed a win on Saturday as he headed into the February 5 "Super Tuesday" contests in two dozen states to have a realistic chance of victory.

The high stakes fueled a week of angry accusations, harsh advertisements and increasingly personal jabs between the two candidates, capped by a volley of attacks on Obama from Clinton's husband, former President Bill Clinton.

Exit polls showed Obama won four of every five black voters in a state where they were expected to be about half of the primary electorate. He also won one-quarter of white votes, higher than many had predicted.

Edwards, the former North Carolina senator, chastised his two rivals for their squabbling and ran ads promoting himself as the grown-up in the contentious nominating battle.

Edwards said the tone of the South Carolina contest was disappointing: "There's been a lot of effort by the other two candidates to tear each other down which is why I'm focused on the voters and doing positive things."

Clinton left South Carolina for two days during the week and headed to states with contests on February 5, leaving her husband to carry the campaign load here.

All three candidates have portrayed themselves as the strongest leaders of a shaky economy. Clinton has hammered Obama for a lack of experience and highlighted her readiness to lead "from day one" in the White House.

But Obama questioned her judgment on Friday, noting her vote in 2002 to authorize the Iraq war and her failed stewardship of the health-care overhaul during Bill Clinton's administration.

"It's not a question of being ready on day one," he said at an evening rally in Florence, South Carolina. "It's a question of being right on day one."

The Republican presidential contenders, who held their primary in South Carolina last week, are focused on Florida's Tuesday primary.

Arizona Sen. John McCain and former Massachusetts Gov. Mitt Romney are in a tight race in Florida, polls show, after splitting contests last week -- McCain won South Carolina and Romney won Michigan.

Former New York Mayor Rudy Giuliani is desperately seeking a good showing that could get him back in the race. Giuliani, who once led the Republican field in national polls, has slipped after he essentially pulled out of the early voting states to concentrate on Florida." (John Whitesides, Reuters, January 26, 2008)

(Additional reporting by Ellen Wulfhorst, Tim Gaynor, Deborah Charles, Jason Szep; Editing by Peter Cooney)