Hillary Clinton beat rival Barack Obama in Pennsylvania on Tuesday, prolonging an increasingly negative Democratic presidential race and keeping alive her slim White House hopes.

Clinton led 55 percent to 45 percent with more than 85 percent of the vote counted, a strong showing but probably not enough to dramatically change the race or narrow Obama's lead in delegates who select the Democratic nominee at the August convention.

The New York senator survived a heavy advertising onslaught by Obama, who outspent her by more than 2-to-1 in the first Democratic nominating contest in six weeks.

"Some people counted me out and said to drop out, but the American people don't quit and they deserve a president who doesn't quit either," Clinton told cheering and chanting supporters in Philadelphia.

Clinton, whose campaign is in debt and running low on cash, urged backers to visit her Web site and donate.

"The future of this campaign is in your hands," said Clinton, who was joined on stage by her husband, former President Bill Clinton, and daughter Chelsea.

The contest in Pennsylvania, where 158 delegates were at stake, opened the final phase of the Democratic duel for the right to face Republican John McCain in November's presidential election. Nine more contests are scheduled before the voting ends on June 3.

The race moves on to contests on May 6 in North Carolina, where Obama is favoured, and Indiana, where the race is more of a toss-up. Obama already was looking beyond Pennsylvania, leaving the state for an evening rally in Indiana. - Reuters