DENVER - MRS Hillary Clinton offered a rousing plea for Democratic Party unity on Tuesday, promising to work for Mr Barack Obama and challenging her supporters to bury their grudges and rally behind his White House bid.

'The time is now to unite as a single party with a single purpose,' said Mrs Clinton, adding she could not sit on the sidelines and watch Republican presidential candidate John McCain 'squander the promise of our country.'

Are Clintons leaving the national scene? DENVER - THIS week at Mr Barack Obama's big party in Denver, Americans are watching Democrats Bill and Hillary Clinton pass from the national stage, at least for now, and all indications are that it is a difficult departure. It has been a long time at the top, 16 years in which they dominated Democratic national politics, first from his perch at the White House with her as first lady, then her seven years as a senator from New York and Democratic presidential candidate. ... more

'No way, no how, no McCain. Barack Obama is my candidate and he must be our president,' Mrs Clinton said in a highly anticipated moment in the spotlight at the Democratic convention.

Her enthusiastic call for party unity was designed to end a rift that has clouded the convention to nominate the first-term Illinois senator to face Mr McCain in the Nov 4 election.

'When Barack Obama is in the White House, he'll revitalise our economy, defend the working people of America, and meet the global challenges of our time,' Mrs Clinton told a roaring crowd waving a sea of white 'Hillary' signs.

Her husband, former President Bill Clinton, watched from the balcony.

The second day of the convention focused on economic themes and began to discuss Mr Obama's plans to aid lower- and middle-class voters suffering in a faltering US economy, which polls show is the top issue in the final months of President George W. Bush's term.

The convention's keynote speaker, filling the role that shot Mr Obama to political fame at the Democratic convention in Boston in 2004, was former Virginia Gov Mark Warner.

'At this critical moment in our history, we have one shot to get it right, and the status quo just won't cut it,' said Mr Warner, favoured to win his race for the US Senate this year.

Mr Warner, a moderate who had success winning over rural voters in normally Republican areas, said Obama and Democrats had to reach across party lines to find success.

'We need leaders who see our common ground as sacred ground,' he said. 'We need leaders who will appeal to us not as Republicans and Democrats, but first and foremost as Americans.'

The drama around Mrs Clinton and the lingering anger of her supporters after their bruising nominating fight meant her speech would be watched closely for her level of enthusiasm and degree of sincerity.

Mr Obama, 47, had tried to ease the lingering tension by giving Mrs Clinton, a New York senator, and her husband major roles at the convention. Mr Bill Clinton will address the Democrats on Wednesday.

Mrs Clinton visited the convention podium on Tuesday afternoon to scout out the arrangements. Asked if she was excited about the speech, she said: 'You bet.'

Some of Tuesday's speakers cranked up the criticism of McCain at the urging of Democrats who wanted a tougher approach to the Arizona senator. The first night of the convention focused on presenting a softer, more personal side of Mr Obama.

'It's clear: the only thing green in John McCain's energy plan is the billions of dollars he's promising in tax cuts for oil companies. And the only thing he'll recycle is the same failed Bush approach to energy policy,' said Pennsylvania Gov Ed Rendell, a Clinton supporter during the primaries.

Kansas Gov Kathleen Sebelius, at one time considered a possible vice president for Obama, used a reference from the 'Wizard of Oz' to bring up Mr McCain's seven homes.

'I'm sure you remember a girl from Kansas who said there's no place like home. Well, in John McCain's version, there's no place like home. And home. And home. And home,' she said.

Mrs Clinton, 60, is expected to free her delegates to back Obama on Wednesday. She will be formally nominated although a roll call vote by states could be cut short and Mr Obama nominated by acclamation under a deal being negotiated by the two camps.

A daily Gallup tracking poll on Tuesday gave Mr McCain a 2-point national edge over Mr Obama, 46 per cent to 44 per cent, within the margin of error but his first lead since Mr Obama clinched the Democratic nomination in June.

Republicans say Mr Obama is too inexperienced to take on the presidency and they sought to play up the Democratic divisions, releasing a new ad that repeated Mrs Clinton's criticisms of Mr Obama during the primaries. It ended with an announcer saying, 'Hillary's right.' -- REUTERS