Al Gore, long mocked as an exaggerating bore, seems certain to land a lead role at the Democratic National Convention as an internationally recognized defender of the Earth.

Eight years after losing one of the closest White House elections ever, Gore is being embraced by party faithful as the Nobel Peace Prize-winning crusader against global warming, and one of the most successful failed U.S. presidential nominees in history.

While the Democratic Party has yet to announce its lineup of convention speakers, the former vice president is on an anticipated short list of headliners at the four-day gathering in Denver that opens on August 25, party aides say.

"He'll receive a tremendous reception," said Democratic Sen. Tom Harkin of Iowa, a convention delegate.

"A lot of us still feel he was cheated" in the 2000 vote, Harkin said. "If he'd been president, we wouldn't have had these (Bush administration) messes the past eight years."

"Also, we admire his tenacity in protecting the environment. Many share his vision on what needs to be done," Harkin said.

In travelling the world to warn against the threat of climate change, Gore, 60, routinely draws packed crowds and has earned rock-star status among young supporters.

On July 17 in Washington, more than 4,000 crammed into Constitution Hall to hear Gore. Tickets, all free, were snapped up within 24 hours after it was announced he would be there.

"He's charismatic. He's a strong orator. He has a presence that draws you in," George Chipev, a 20-year-old Georgetown University student, said afterward in listing attributes that even Gore backers admit he lacked in his White House bid.

Added Beth Camphouse, 21, a student at James Madison University: "Al Gore is one of the few public figures challenging my generation to do anything. He's inspirational."

In addition to the Nobel Peace Prize that Gore won in 2007, the film version of his slide-show lecture and book on global warming, "An Inconvenient Truth," won an Academy Award for best documentary feature that year. In 2006, he helped found the nonpartisan Alliance for Climate Protection.

STILL HAS CRITICS

After eight years as vice president and 16 years in Congress, Gore has rejected calls to run for office again.

"I don't think I'm very good at some of the things that the modern political system rewards and requires, and I've found other ways to make a difference and to serve the public interests," Gore told his hometown newspaper, the Nashville Tennessean, last year. "And I'm enjoying them."

"You've got to give Al Gore credit," said Shirley Anne Warshaw of the Centre for the Study of the Presidency. "He became a star by rising above politics with his passion for the environment. He's now international leader on an issue more and more people care about. There has been no more successful defeated presidential candidate."

To be sure, Gore still has critics, particularly ones who accuse him of overstating the threat of climate change, despite mounting scientific evidence.

Yet Gore has drawn support on both sides of the political aisle, including Democratic presidential candidate Barack Obama and John McCain, his Republican rival in the November election.

The two embraced Gore's challenge to commit to producing all U.S. electricity from renewable sources like solar and wind power within 10 years in order to get away from carbon-based fuels.

"If the vice president says it's do-able, I believe it's do-able," said McCain. Obama said, "It's a strategy that will create millions of new jobs ... and one that will leave our children a world that is cleaner and safer."

Sen. Jeff Sessions, an Alabama Republican denounced it. "Unless there is some monumental breakthrough, it is not possible," Session said. "It cannot be the basis of a sound energy policy by any responsible official in America, it seems to me. Maybe I am wrong, but I don't think so."

During the 2000 White House race, Gore was ridiculed as stiff and wooden. By contrast, Republican foe George W. Bush, then the Texas governor, came across as far more personable, although not as knowledgeable.

On Election Day, Gore won the popular vote. But Bush took the White House when a divided U.S. Supreme Court let stand his contested 537-vote margin of victory in Florida that allowed him to capture the decisive, state-based Electoral College.

At the 2004 Democratic Convention, Gore joked about it.

"You win some, you lose some and then there's that little- known third category," Gore said, drawing laughter, cheers and tears.

The Pew Research Centre released a poll in May that found 53 percent of Americans had a favourable opinion of Gore, slightly higher than Obama's 52 percent. Bush's approval rating is under 30 percent, battered by the unpopular Iraq war and the ailing U.S. economy.