Friends of Al Gore have secretly started assembling a campaign team in preparation for the former American vice-president to make a fresh bid for the White House.

Mr Gore, President Bill Clinton's deputy, has said he wants to concentrate on publicising the need to combat climate change, a case made in his film, An Inconvenient Truth, which won him an Oscar this year.

His denials of interest in the presidency have been couched in terms of "no plans" or "no intention" - politically ambiguous language that does not rule out a run.

One of his former campaign team said: "I was asked whether I would be available towards the end of the year if I am needed. They know he has not ruled out running and if he decides to jump in, he will have to move very fast.

"He hasn't asked them to do this, but nor has he told them not to."

James Carville, President Clinton's former strategy chief, suggested last week that Mr Gore, who has piled on the pounds, could shed weight over the summer to make himself more media-friendly for a White House run.

"I wouldn't be surprised if he lost 15lb or so," said Mr Carville. "And I think if people thought he could get us out of the mess we're in with Iraq, they wouldn't care how fat he is."

Vice-President Gore's allies believe that Hillary Clinton, 59, the frontrunner, is unable to win the presidency. The most recent poll shows a growing number of voters think negatively of her, in contrast to Mr Gore, who enjoys far greater popularity than when he lost the 2000 presidential race despite polling more votes nationally than the eventual winner, George W Bush.

The second aide approached by Vice-President Gore's allies said: "There is no love lost between Gore and Hillary. They don't think she can win and they're probably right. If Gore runs, he's got a really good chance of getting the nomination. And he has a good chance of pulling off the election, too."

The most recent opinion polls show Mr Gore as third favourite to take the Democratic nomination, on about 17 per cent support, only a whisker behind Barack Obama, 45, who is aiming to become the first black US president, and ahead of John Edwards, 53, the senator whose wife was recently diagnosed with cancer.

A Republican said: "Gore could be the toughest Democrat to beat."

Gore-watchers believe that a new book he is publishing next month on the state of US politics will keep his name in the public eye. Many of his supporters helped to run the unsuccessful presidential campaign of John Kerry in 2004. But since Sen Kerry abandoned his presidential aspirations this year, many of his leading advisers have yet to align themselves with any of the other candidates.

At least eight websites are campaigning to "Draft Gore" into the election. More than 70,000 people have signed an online petition, and more than 120 groups of Gore supporters meet each month around the country to promote the case for a Gore presidency. One website offers the chance to download a song called Run Al, Run!