Hillary Clinton ordered her grieving supporters to unite behind Democratic nominee Barack Obama, in an emotional final act to her White House quest which fell just short of history.

"Whether you voted for me, or voted for Barack, the time is now to unite as a single party with a single purpose," said Clinton, who got a euphoric welcome for her primetime speech Tuesday at the Democratic National Convention.

"We are on the same team, and none of us can sit on the sidelines," she said, vowing to work to elect the man who thwarted her presidential dreams, and who will make his own history by becoming the first black presidential nominee.

The former first lady milked a deafening ovation as the crowd, blanketed with signs bearing a stylized version of her "Hillary" signature, feted her almost as though she had won the exhausting primary fight.

She told the thousands in the arena, and millions of her army of women and blue-collar voters watching on television, that despite their fierce primary duel, "Barack Obama is my candidate. And he must be our president."

Wistfully, Clinton looked back on the thousands of miles, and thousands of speeches and meetings that made up her presidential campaign, which finally ended when Obama clinched the nomination in June.

"You taught me so much, you made me laugh and ... you even made me cry. You allowed me to become part of your lives, and you became part of mine."

Senator Obama watched Clinton's speech from Montana, and hailed her oration as an "outstanding" appeal for Democratic unity.

"That was excellent, that was a strong speech. She made the case for why we're going to be unified in November and why we're going to win this election."

Clinton also lashed Republican White House hopeful John McCain as a "twin" of unpopular President George W. Bush, saying he stood for "more war, less diplomacy," and "more economic stagnation, less health care."

The former first lady, introduced by daughter Chelsea, said she had not spent the past "35 years in the trenches" to suffer more "failed leadership" from Republicans.

"No way, no how, no McCain," she said.

The New York senator, however, did not say that Obama was ready to serve as commander-in-chief and sought a political rather than personal connection with the new party champion.

The McCain campaign seized on the omission.

"Senator Clinton ran her presidential campaign making clear that Barack Obama is not prepared to lead as commander in chief," McCain spokesman Tucker Bounds said.

"Nowhere tonight, did she alter that assessment, nowhere did she say that Barack Obama is ready to lead," he said.

"Millions of Hillary Clinton supporters and millions of Americans remain concerned about whether Barack Obama is ready to be president."

Clinton's speech was closely scrutinized for her willingness to heal the wounds of a primary campaign which split the Democratic Party in two, and offered hopes to Republicans in a tough year for the demoralized party.

But she gave her blessing to Obama in the first lines of her speech, providing valuable television pictures of an arena of cheering Democrats united, after a compelling nominating battle.

Clinton's 18 million primary voters are vital to Obama, as his White House race with McCain has tightened to a dead heat.

In an effort to forge party unity, Clinton was expected to release her delegates, freeing them to vote for Obama in Wednesday's roll call vote.

The speech was the first of a one-two punch from the Clintons -- former president Bill Clinton will address the convention on Wednesday -- after fighting a barely disguised feud with the Obama campaign.

After her speech, Clinton sent an email to supporters urging them to help Obama win the election.

"Standing on that stage tonight in front of 20,000 Democrats unified behind Senator Obama, I saw a bright future for America," she wrote.

"I saw millions of people across the country working as one to elect the next Democratic President."

Moses Ross, a delegate from Portland, Oregon, said he would support Obama because "Hillary Clinton has asked me to."

"I'm sad that we're not standing here talking about her running for president, but we have to abide by her wishes."