The long and often bitter contest appeared to be nearing its climax, with Obama, a 46-year-old first-term senator, recovering from weeks of turmoil and poised to defeat one of the most powerful names in American politics.

Clinton signalled her determination to fight on, but her prospects seemed dim. In Tuesday's primaries, Obama expanded his lead among delegates who will choose the party's nominee. Clinton will have few opportunities to make up the difference in the remaining six contests.

Clinton's campaign funds are low and her weak showing in Tuesday's election could make it difficult for her to replenish her coffers. It will also make it harder to persuade superdelegates - the party and elected officials who can support whomever they choose at the party's national convention - to swing the nomination in her favor.

Returns from 99 percent of North Carolina precincts showed Obama winning 56 percent of the vote to 42 percent for Clinton, a triumph that mirrored his earlier victories in southern states with large black populations.

In the midwestern state of Indiana, returns from 99 percent of the precincts showed Clinton with 51 percent to 49 percent for the Illinois senator, a margin of little more than 22,000 votes out of more than 1.2 million cast. The outcome was not clear for more than six hours after the polls closed, the uncertainty stemming from slow counting in Lake County near Obama's home city of Chicago.

Obama won at least 94 delegates and Clinton at least 75 in the two states combined, with 18 still to be awarded.

"Tonight we stand less than 200 delegates away from securing the Democratic nomination for president of the United States," Obama told a raucous rally in Raleigh, North Carolina.

Clinton, joined at her ally by her husband Bill and their daughter Chelsea, pledged to continue her quest to become the first female U.S. president, telling cheering supporters in Indianapolis, "Thanks to you, it's full speed to the White House."

And she declared anew that she would support the Democratic nominee "no matter what happens," a vow also made by her competitor.

Obama, an inexperienced but charismatic senator, stunned the political establishment by winning 11 consecutive contests in February. But he repeatedly failed to knock Clinton out of the race, as she won major primaries in March and April.

Some Democrats worried whether Obama's defeats indicated that he could not attract the white, working-class voters needed for their party to win in the November election against Republican John McCain. They feared they might be squandering an opportunity to capture the White House after the unpopular presidency of George W. Bush, a Republican.

For weeks, Obama's campaign has been bogged down as he struggled to explain remarks about "bitter" working-class voters, his relationship with a controversial pastor and why he does not wear a U.S. flag pin on his lapel.

At his North Carolina rally, he told supporters that his win was a victory against the "politics of division and the politics of distraction."

Obama acknowledged there were "bruised feelings on both sides" in the nomination battle, but predicted Democrat would be united for the November election.

"We can't afford to give John McCain the chance to serve out George Bush's third term," Obama said.

Obama's delegate haul edged him closer to the nomination. Obama led with 1,840.5 delegates, including separately chosen party and elected officials known as superdelegates. Clinton had 1,684 delegates.

Obama was 184.5 delegates shy of the 2,025 needed to secure the Democratic nomination at the party's convention this summer in Denver.

With only 217 delegates at stake in the final six contests, Clinton has almost no chance of winning enough elected delegates to overtake Obama. She would need strong support from the 220 superdelegates who remain undecided and 50 more who will be named later.

The campaign has been dominated by the weak U.S. economy which was by far the top issue in North Carolina and Indiana, according to interviews with voters as they left polling places. Record-high gas prices are a huge concern across the car-loving country.

The candidates sparred in recent days over Clinton's call for a temporary suspension of the federal gasoline tax this summer.

Clinton said it would help beleaguered drivers; Obama ridiculed the proposal as a political stunt that would cost jobs.

To a large extent, the gasoline tax eclipsed the attention surrounding the Rev. Jeremiah Wright, Obama's former pastor whose fiery rhetoric angered and insulted many Americans. After saying several weeks earlier that he could not disown Wright, Obama did precisely that when the minister embarked on a media tour and repeated his controversial remarks.

Voters in both states were divided evenly when asked whether the controversy surrounding Wright was a factor in their decisions.

Racial divisions were stark

In both states, Clinton won six in 10 white votes while Obama got nine in 10 black votes, exit polls indicated. But blacks comprised about a third of the voters in North Carolina - nearly double their proportion in Indiana.

Polarizing, protracted and often bitter, the contest is hardening divisions in the party, according to exit polls from the two states.

A solid majority of each candidate's supporters said they would not be satisfied if the other candidate wins the nomination.

Fully one-third of Clinton's supporters in Indiana and North Carolina went beyond mere dissatisfaction to say they would vote for McCain instead of Obama if that is the choice in the fall.

Against the backdrop of disunity, pressure is certain to intensify on the superdelegates to declare themselves so the party can get together behind its nominee for the campaign against McCain.

They are not bound by results in primaries or caucuses.

"There is an eagerness in the party to get this done and move on," said David Axelrod, chief Obama strategist. "There is no question that we can see the finish line."