Denver, Colorado (dpa) - Anyone who expected Hillary Clinton to bow gracefully from the scene or be a sore loser may want to think twice after the heartfelt endorsement she delivered for her onetime rival Barack Obama for US president.

The former first lady, 60, made a grand, triumphant entry into the Pepsi Center convention hall Tuesday evening, creating a din of shouts, cheers and whistles among the 4,400 delegates gathered to nominate Obama.

Her audience whipped out large white Hillary signs that nearly covered up crowd, waving them while they shouted. One may have even thought she had won the nomination - or was setting the stage for some nominating convention in the future.

The roar died down after three minutes, only to rise again after her declaration that she was a "proud supporter of Barack Obama."

"Whether you voted for me, or voted for Barack, the time is now to unite as a single party with a single purpose. We are on the same team, and none of us can sit on the sidelines," the New York Senator said.

Clinton said electing Obama president on November 4 over presumptive Republican nominee John McCain was a "fight for the future" at a time when centre-left Democrats must "take back the country we love."

Her nationally-broadcast 23-minute address was interrupted loudly and often with more deafening roars, cementing her star status in the party and importance to Obama in drawing in women and blue-collar workers who have been reluctant to support him.

Clinton has been campaigning for Obama since June, when she conceded her historic, hard-fought bid to the African-American senator from Illinois.

Yet much weighed on her convention speech.

She had to convince her diehard supporters and 18 million primary voters to release their bitterness and overcome lingering resentment that has prompted many to say they will not vote for Obama.

And she had to avoid stealing the show from Obama, who will deliver his acceptance speech Thursday night before a throng of 75,000 at Denver's Invesco stadium.

Few women as powerful as Clinton have ever been in such a situation of begging their supporters to back someone else.

Clinton, 60, said she had run for the Democratic nomination "to stand up for all those who have been invisible to their government for eight long years" under US President George W Bush.

"Those are the reasons I support Barack Obama. And those are the reasons you should too,"she said.

In a salute to her supporters and voters who sent more than 40 per cent of the party's delegates to the four-day convention, she recalled dramatic moments from the primary season.

She spoke of a cancer-afflicted mother of two autistic children who had painted Hillary's name on her shaven head "and asked me to fight for health care."

The convention hall erupted in laughter when she tipped her hat to the "sisterhood of the traveling pantsuits" who had stood by her during the gruelling year-long bid for the nomination.

Then Clinton turned serious, urging them to ask themselves the question: "Were you in this campaign just for me?" Or were they in it for the cause of affordable health care and people struggling against "jobs lost, houses gone, falling wages, rising prices?"

It was not clear if her speech had convinced all of her delegates in Denver.

Clinton is expected to meet with them Wednesday afternoon and ask them one final time to support Obama in the evening's state-by-state roll call vote that could be cut short under party rules if there is a unanimous acclimation for Obama.

The message of the need to knock on doors and make phone calls for Obama got through to at least one of Clinton's loyal campaign workers, Allida Black of Virginia, who said she had worked for 19 months, across 14 states and emptied her savings for Clinton's campaign.

"The speech was out of the ball park," Black told Deutsche Presse-Agentur dpa. It was "fierce" and "passionate."

"She gave us our marching orders," Black said. "This is not about us."

But Black also said she would push for a full roll-call vote, and so should the Obama campaign, because delegates had shown the "tremendous unity in the true spirit of the party" with their emotional reception for Clinton.

"That would allow us to throw ourselves heart and soul into the Obama campaign afterwards," she said.