WASHINGTON, D.C. -- With an eye toward healing a divided Democratic Party while affirming the historic significance of her own campaign, Sen. Hillary Rodham Clinton yesterday ended her year-and-a-half quest to become the first woman to win the White House.

She vowed to "work my heart out" for Sen. Barack Obama in his own groundbreaking bid to become the nation's first African-American president.

In a 30-minute speech that was part thank-you, part pep rally, part elegy, Mrs. Clinton congratulated her former opponent on "the victory he has won and the extraordinary race he has run. I endorse him, and throw my full support behind him."

After a lighthearted beginning -- "This isn't exactly the party I'd planned but I sure like the company" -- she urged the crowd at the National Building Museum "to take our energy, our passion and our strength and do all we can" to restore a Democrat to the White House in November.

"Today I am standing with Sen. Obama to say, 'Yes we can,'" she said, citing Mr. Obama's trademark campaign mantra, to cheers from diehard supporters.

Yet there were scattered boos, too, at the mention of her rival's name -- only serving to underscore the fractured state of the party after one of the closest, most bitterly fought primary contests in U.S. political history, something Mrs. Clinton seemed to acknowledge when she urged her followers to look forward.

"When you hear people saying, 'What if, if only,' please -- don't go there," she said.

"Every moment wasted looking back keeps us from moving forward. Life is too short, time is too precious, and the stakes are too high to dwell on what might have been," she told the audience of more than a 1,000 people, some of them in tears.

In this "turning point" of an election, she added, "it is critical that we all understand what our choice really is. Will we go forward together or will we stall and slip backwards?" Standing under 89-foot columns in the Great Hall of the museum, which was built in the 19th century to house work on pensions for Civil War veterans, Mrs. Clinton was accompanied by her husband, former President Bill Clinton, her mother, Dorothy Rodham, and her daughter, Chelsea Clinton.

Speaking with an eye not just toward her own political future but to her husband's legacy -- somewhat scratched and dented in the rough and tumble of the campaign -- she noted only three presidential elections out of 10 had been won by Democrats in the past 40 years, and "the man who won two of those elections is with us today," then turned and applauded him.

To a greater extent, perhaps, than during the campaign, Mrs. Clinton also talked about the role that gender plays in American politics -- for good or ill. She acknowledged "the barriers and biases out there, often unconscious," against women today, she recalled suffragettes first gathering in Seneca Falls, N.Y. in 1848, and she thanked women in their 80s and 90s "born before women could vote, who cast a vote in our campaign."

"Although we weren't able to shatter that highest, hardest glass ceiling this time, thanks to you, it's got about 18 million cracks in it," she said in a not-so-subtle reference to the 18 million votes she received in one of the tightest primary races in history. "And the light is shining through like never before, filling us all with hope and the sure knowledge that the path will be a little easier next time."

"From now on, it will be unremarkable for a woman to win primary state victories, unremarkable to have a woman in a close race to be our nominee, unremarkable to think that a woman can be the president of the United States. And that is truly remarkable."

Still, some of those cheering her on were clearly still bitter about the closeness of the race and what they perceived as sexist treatment of their candidate in the media and on the campaign trail -- from the shots of "iron my shirt" to the Hillary nutcracker.

"I am an avid supporter of Hillary's" said Darla Stone, 63, of Culpepper, Va. "She'll probably get over this faster than I will. The media did her a great disservice and gave him a free ride," she said, adding that "they always published the ugliest photos of her. Why is that?"

Mrs. Stone, who works at Coffeewood Correctional Center in central Virginia, said she would rather vote for Republican John McCain than Mr. Obama, whom she called "an elitist. And I'm not alone. I work in a men's prison with blacks and Latinos who feel the same way I do."

She dismissed the notion of Mrs. Clinton as Mr. Obama's running mate.

"It's a subordinate role. It's like being elected class secretary. I don't think I can stomach that," she said.

Sandy Ogas, of Annapolis, Md., was more conciliatory -- her husband, John Ogas, is an Obama supporter and the couple decided to make a show of unity at the event.

"What makes me really sad is that I'll probably die without seeing a woman as president," she said. "The country just didn't want a woman, and at the rate we're going it will be another 200 years before one of us gets in the White House," she said, while Mr. Ogas rolled his eyes.

"I don't argue with my wife in public, but the important thing is that Hillary Clinton is here today uniting the party behind Obama," he said.

Mrs. Clinton's journey from front-runner to also-ran began in January 2007, when she announced in a video posted on her Web site that she was "in it to win it," and indeed, she was leading in the polls, fund raising and endorsements.

But a few dramatic early victories never materialized; instead, she stumbled after a third-place loss in the Iowa caucuses early this year. Despite Ms. Clinton's surprise win in New Hampshire, Mr. Obama's victories in 11 straight primaries gave him a delegate lead she could not surmount.

On Tuesday, Mr. Obama finally claimed the nomination after a flood of superdelegates announced they were supporting him and final primaries in Montana and South Dakota gave him the 2,118 delegates he needed.

That evening, Mrs. Clinton declined to concede, saying she needed more time to talk with party leaders. But two days later she announced she was endorsing Mr. Obama and suspending her campaign -- but not ending it, so that delegates still being slated at various state conventions would be allowed under party rules to go to the Democratic National Convention in August.

Mr. Obama and Mrs. Clinton met secretly for an hour Thursday night at the Washington home of Sen. Dianne Feinstein, D-Calif., an early supporter of Mrs. Clinton, and afterward issued a joint statement saying they had discussed the campaign without providing more details.

While clearly signaling her political career isn't over, Mrs. Clinton made no mention in yesterday's speech of any interest in being Mr. Obama's running mate, despite saying earlier last week she was "open" to it. But it's expected she will seek his help in retiring the $30 million debt she incurred during the nomination marathon.