The Associated Press declared Clinton the winner less than an hour after the polls closed. Early returns showed the former first lady was gaining more than 60% of the vote.

According to an AP analysis of the early returns, Clinton won at least 28 delegates of the 55 at stake in Puerto Rico while Obama won at least 14, with 13 still to be allocated. That brings the Illinois senator tantalizingly close to the 2,118 needed for the nomination.

Clinton campaigned even into Sunday in an apparent attempt to pick up as much of the popular vote as possible during the waning days of the primary calendar to try to demonstrate her vote-getting appeal to Democratic party figures.

Obama, speaking at a rally in Mitchell, S.D., late Sunday congratulated Clinton on her victory in Puerto Rico, calling her "an outstanding public servant."

He also said that supporters of both candidates would unite for the fall election, but made it clear that he expects to be the party's standardbearer.

"She is going to be a great asset when we go into November to make sure we defeat the Republicans, that I can promise you," Obama told the crowd.

The Clinton victory, while sizable, was largely symbolic. Puerto Rico, where the island's residents — all U.S. citizens — cannot vote in the November general election.

The win did demonstrate Clinton's strength among Hispanic voters, who have supported her over Obama in contests aleady held in states such as California, Arizona and Texas.

But the bid for the presidential nomination has come down to the delegates, and the need to appeal to so-called superdelegates, the party leaders who are free to choose regardless results in primaries.

On Saturday, the Democratic Party's Rules and Bylaws Committee agreed to give disputed delegates from Florida and Michigan a half vote each at the party's nominating convention in Denver. The decision angered Clinton and did little to help her close the lead Obama has on delegates needed to clinch the nomination.

With the panel's decision, which took place on the eve of the Puerto Rico election, Obama had 2,052 delegates and Clinton had 1,877 delegates.

The Clinton campaign accepted the Florida decision, but objected to the terms of the Michigan settlement.

"This decision violates the bedrock principles of our democracy and our party," Clinton's campaign said in a statement by Harold Ickes and Tina Flournoy, two of her advisers. Ickes said on NBC's Meet the Press on Sunday that Clinton had reserved the right to take the fight to the party's credentials committee or even to the convention in Denver in August.

A spokesman for the Obama campaign said the Illinois senator could secure the nomination this week, perhaps as early as Tuesday, after the Montana and South Dakota contests.

"If not Tuesday, I think it will be fairly soon," Obama spokesman Robert Gibbs said Sunday on ABC's This Week.

The biggest remaining bloc of votes is made up of party leaders known as superdelegates who are free to choose regardless of results in primaries. Many had been reluctant to declare a preference until after completion of all the primaries and caucuses.

Clinton campaign spokesman Mo Elleithee said Clinton is trying to persuade superdelegates that she would be stronger against presumptive Republican nominee john McCain.

"We're making our case to them every day," he said. "She is focused on winning the nomination, we believe there is a path to winning the nomination, and while Senator Obama has a lot of advantages right now, not everyone has had their say in this race and she is out there working harder than anyone to make the case."

Clinton stopped into the Kastela Bakery on Sunday morning to shake hands and pick up a cafe con leche and a pastry.

She had a supporter in Virginia Guevara, who was having her regular Sunday breakfast. "She's the one that's been taking care of Puerto Ricans since Clinton's presidency," Guevara said. "She was with us when the hurricane hit. She considers herself one of us."

As for Obama, Guevara said, "we don't know him."

Voting in the primary is important even though she can't vote in November "to spread the word that we're interested in the process," says Guevara, who favors statehood for Puerto Rico.

Her brother, Victor Ernesto Guevara, favors Obama and opposes statehood. "I don't think we should be voting in the primary. We shouldn't be getting into the U.S.'s business — and vice versa," says the brother, who was visiting from Amherst, Mass.

Clinton's high profile here is due, in part, to the popularity of former President Bill Clinton. As a senator from New York, Clinton represents some 1 million Puerto Ricans who now live in the Empire State. She has worked on issues key to Puerto Ricans, such as ending the Navy's bombing on the island of Vieques.

While she has not taken sides on the longstanding issue of statehood, she promises to get the issue resolved in her first term as president. Obama has made a similar pledge.

"I also will work to make sure that the people of Puerto Rico have the right to decide by majority vote what your future status should be," Clinton told some 6,000 members of the Congregacion Mita, a homegrown Puerto Rican Christian denomination, at a church service Saturday evening.

"From day one of my presidency, I will work with all factions and with the congress without preference or any option to give you the right to make that decision. And that I will work to implement that decision," she said.

Clinton kicked off a weekend of campaigning Friday night with a rally, then rode onthe back of a pickup around San Juan's suburbs all day Saturday.

"Campaigning in Puerto Rico is like one long Puerto Rican Day parade," she said cheerfully on Saturday, invoking the annual New York City event that draws big crowds and plenty of politicians.