The announcement pits two influential Democratic families - the Kennedys and the Clintons - against each other, and increases pressure on Mrs Clinton after Senator Obama's decisive win in the South Carolina primary Saturday.

In the Republican race, Mitt Romney and John McCain accused each other of being closet liberals on Monday, a day before a key contest in Florida. Such a charge bordering on blasphemy among conservative Republicans in the increasingly caustic campaign for that party's presidential nomination.

With split decisions in the Democratic contests so far - Senator Obama won Iowa and South Carolina, Mrs Clinton won New Hampshire and Nevada - there is increased speculation that the race will extend beyond the Feb 5 22-state mega-contest known as Super Tuesday. Senator Obama needs to steadily build on his newfound momentum if he is to upstage Mrs Clinton and become the first black US president.

'Man with extraordinary gifts'
Mr Kennedy endorsed Senator Obama on Monday as a 'man with extraordinary gifts of leadership and character,' and a worthy heir to his brother, former President John F. Kennedy, who is still revered among Democrats four decades after his assassination. According to several associates, he became angered with what he viewed as racially divisive comments by former President Bill Clinton.

'I feel change in the air,' Mr Kennedy said at a crowded rally at American University in Washington.

He was joined by his son, Representative Patrick Kennedy, and introduced by Caroline Kennedy, daughter of the late president, who had already endorsed Senator Obama in a piece for the New York Times.

'Today isn't just about politics for me. It's personal,' Senator Obama, 46, said at the rally. 'I was too young to remember John Kennedy and I was just a child when (his brother) Robert Kennedy ran for president. But in the stories I heard growing up, I saw how my grandparents and mother spoke about them, and about that period in our nation's life - as a time of great hope and achievement.'

Close the gap
Mr Kennedy's support could help Senator Obama close the gap before Super Tuesday, and his endorsement was sought by all the Democratic candidates. Besides his status as a liberal icon and member of the Kennedy dynasty, Mr Kennedy boasts a broad national fundraising and political network as well.

Earlier on Monday, Nobel Prize-winning author Toni Morrison, who famously labelled Bill Clinton as the 'first black president' also endorsed Senator Obama.

Mrs Clinton, however, relegated Senator Obama to the rhetorical sidelines as she focused her criticism on President George W. Bush, saying he had lost touch with the economic concerns of an anxious public as he gives his last State of the Union address Monday.

'It is the last time George Bush will give the State of the Union. Next year it will be a Democratic president giving it,' she told a cheering crowd of about 1,000 in Connecticut.

President Bush is certain to assert that the state of the nation is strong even though 'we are sliding into a recession. We have as lot of concerns we need to deal with,' including a mortgage crisis that is driving people from their homes, she said.

The senator also picked up the endorsement of Senator Bill Nelson of Florida, which holds its primary on Tuesday. Like all of her Democratic rivals, Mrs Clinton has agreed to a pledge imposed by national party leaders not to publicly campaign there because of a dispute between state and national party officials over the timing of the primary.

The vote now offers no delegates to the Democrat convention that chooses the party's presidential nominee.

Mrs Clinton has already reached out to Florida residents by saying she believes their delegates should count.

Republicans
Meanwhile, Republicans battled it out over Florida. Mr Romney, a former venture capitalist and Massachusetts governor, slammed Mr McCain, looking to portray the veteran Arizona senator who leads in national polls as out-of-step with the Republican Party's conservative policies.

He blasted Mr McCain's 2002 campaign finance reform bill, a failed immigration bill last year that would have allowed illegal immigrants to remain in the country indefinitely, and a 2003 energy bill to reduce pollution by power plants and oil refineries that he said would increase energy costs for families.

'Those aren't conservative, those aren't Republican, those are not the kind of leadership we need as we go forward,' he told reporters.

Mr Romney has cast himself as a business-savvy economic turnaround artist amid recession anxiety, while Mr McCain, a former Vietnam prisoner of war, portrayed himself as a courageous wartime commander-in-chief in a dangerous world.

Mr McCain answered Mr Romney swiftly in a statement. He accused the former Massachusetts governor of 'wholesale deception of voters. On every one of the issues he has attacked us on, Mitt Romney was for it before he was against it.'

Neck-and-neck
The exchange reflected the stakes for Republicans in Tuesday's Florida contest. Mr McCain and Mr Romney are leading neck-and-neck in the Florida polls among Republicans, with Giuliani, a former New York City mayor, well behind. Preacher-turned-politician Mike Huckabee, the Iowa caucuses winner for the Republicans, was also lagging in the polls.

Acrimony has replaced the recent civility of the Republican race.

The Romney campaign said voters have been receiving automated phone calls that say Mr Romney supports taxpayer-funded abortions and opposes President Bush's tax cuts, neither of which is true. Another set of calls from an unknown critic claim Romney favours direct talks with Cuban leader Fidel Castro, said Mandy Fletcher, Mr Romney's Florida campaign director.

The McCain campaign said it was not responsible for the calls.

Florida offers the Republican winner 57 delegates and a shot of energy heading into Super Tuesday, when more than 1,000 delegates will be at stake, a substantial boost to the 1,191 needed to win the nomination at the party's convention.

Trailing behind Senator Obama and Mrs Clinton in the Democratic race was former Senator John Edwards, who has yet to win any of the early state contests. His loss in his birth state of South Carolina was a sharp setback, but he has vowed to stay in the race. -- AP

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