Denver: Democrats made history on Wednesday when they chose Barack Obama as the first black presidential nominee of a major political party.

Obama and his onetime principal rival for the nomination, Senator Hillary Clinton of New York, were both picked up, paving the way for the traditional roll call of state delegations.

In a bit of careful political choreography, after 31 states and territories had announced their votes, the delegation from Obama's home state of Illinois yielded to New York's delegation, and the microphone was passed to Clinton.

"Madam Secretary, on behalf of the great state of New York, with appreciation for the spirit and dedication of all who are gathered here; with eyes firmly fixed on the future; in the spirit of unity with the goal of victory; with faith in our party and in our country: Let's declare together, in one voice, right here and right now, that Barack Obama is our candidate and he will be our president," Clinton said.

Clinton then moved that the roll call be suspended and Obama be nominated by acclamation, which was accepted by whoops, cheers and the chants of "Hillary!" from the New York delegation.

After House Speaker Nancy Pelosi, co-chair of the convention, declared that Clinton's motion had passed, the band erupted into the opening strains of the O'Jays' "Love Train". Delegates held hands, swayed to the music and chanted "Yes we can", one of the Obama campaign's slogans. Later, the crowd chanted "O-ba-ma", after Pelosi told the crowd that the senator would accept the nomination and speak to them.

Earlier, former President Bill Clinton forcefully endorsed Obama's bid for the White House, telling delegates that Obama is "ready to lead America and restore American leadership in the world", reported AP.

Bill's endorsement

Bill Clinton pushed back on attacks that Obama is ill-prepared for the White House, especially on matters of national defence.

But he also suggested that on such weighty issues, Obama would be leaning on his seasoned vice-president, six-term Senator Joe Biden.

Bill Clinton had campaigned feverishly for his wife, Hillary, in her long-fought primary battle against Obama, and took her loss hard. He had not spoken out as strongly in support of Obama since he clinched the nomination in June.

Obama arrived in the city on Wednesday afternoon after a day of campaigning in Montana. He will formally accept the nomination, for which he fought since early last year, in a rally with tens of thousands of supporters at the Denver Broncos football stadium.

Clinton's motion to nominate Obama by acclamation had been expected. Earlier, in a symbolic gesture, Clinton met with many of her delegates and released them to vote for Obama.

Clinton's actions on Wednesday follow her rousing speech on Tuesday night in which she called for unity and for stopping likely GOP presidential nominee John McCain, set to be nominated at his party's convention next week.

One of the plot lines here has been the possibility that Clinton supporters might refuse to back Obama; Clinton again tried to reassure her delegates that it was important to vote for Obama and not bolt to McCain. "After this long journey we've been on," some of you "want the chance to vote what's in your heart. Still others will be voting for Senator Obama because they want to demonstrate their personal commitment to unity of this party behind our nominee. So I am not telling you what to do," she said.

The outcome of the roll call of states - often a device for local officials to tout the wonders and economic possibilities of their states to a national TV audience - has been known for months. After Obama and Clinton's coast-to-coast primary and caucus battles, Obama won enough delegates to clinch the nomination.

New leadership

Clinton, seeking to become the first woman to become president, came in a close second. Obama was nominated by Michael Wilson of Florida, a Republican who was an Air Force medic in Iraq. Obama will be "a president who has the judgment to use war as a last resort, not a first resort", Wilson said. "Obama will be a president who can adapt to new situations as things change."

"You know there's an old saying. 'If you do what you always did, you'll get what you've always got', " Wilson added. "America needs new leadership in the White House, and that leader is Barack Obama."

"It is my distinct honour as an Iraq war veteran, as a lifelong Republican and as a proud citizen of this democracy to nominate the next president of the United States, Barack Obama."

Meanwhile, in a major address on foreign policy at Georgetown University in April, Biden accused the administration of mishandling the war on terrorism, turning "a deadly serious but manageable threat - that is, a small number of radical groups that hate America - into a 10-foot-tall existential monster that dictates literally every move we make".

Biden added, "We cannot afford another four years of Republican stewardship of our national security" - a theme that will likely factor in Wednesday's speech.

Mindful of the Democrats' theme of the night, Republicans sought to undercut their message and portray Democrats as wrong on foreign policy. The McCain campaign unleashed a new television ad quoting Obama as saying Iran "doesn't pose a serious threat" and calling the Illinois senator "dangerously unprepared to be president".

Obama has said Iran does not pose a serious threat in the same way that the Soviet Union posed a serious threat to US national security during the Cold War.

Asked to defend the ad, former New York mayor Rudolph W. Giuliani said that either way, Obama's statement was "a big mistake". Giuliani was in Denver as part of the GOP's rapid-response campaign against Obama.

On the campaign trail on Wednesday, Obama also talked with military families and veterans in Billings, Mont. Obama promised to increase resources for veterans' care.