WASHINGTON — Al Gore, the Democrats' nominee for the White House in 2000, says he has all but ruled out running for president in 2008, saying the best use of his time is to educate people about global warming.

"I haven't made a Sherman statement, but that's not an effort to hold the door open. It's more the internal shifting of gears," said Gore, referring to U.S. Civil War-era general William Tecumseh Sherman. "I can't imagine any circumstances in which I would become a candidate again. I've found other ways to serve. I'm enjoying them."

Gore referred to Sherman's famous words upon retiring from the army in 1884, which put to rest talk of a presidential run: "If nominated I will not run; if elected I will not serve."

Gore in a TV interview stopped short of issuing such an equivocal statement. But he said his time is best spent educating people on heat-trapping gases raising the Earth's surface temperature. He's promoting An Inconvenient Truth, a film that chronicles his intricate slide shows on global warming.

Senator Joseph Biden (D-Del.), who is planning a run in 2008, said Gore would be a strong candidate if he decided to enter the race.

"He would be viable, and he would be welcome," Biden said. "It would add to the debate in this party to have him."

Regarding his own prospects, Biden said he doubted that his vote to authorize the war in Iraq would be a main issue for him or for Senator Hillary Clinton (D-N.Y.), who voted likewise, should she also seek the Democratic nomination in 2008.

On Friday, Senator Edward Kennedy, a prominent Democrat, declared his vote against the Iraq war the best he has cast since being elected in 1962.

Regarding his own vote, Biden said Sunday, "I think misunderstanding this administration was the worst calculation I ever made."

Gore, vice-president from 1993 to 2001, ran unsuccessfully for the Democratic nomination in 1988 and narrowly lost the 2000 presidential campaign to George W. Bush, despite collecting more popular votes than the Texas Republican.

"I honestly believe that the highest and best use of my skills and experience is to try to change the minds of people in the U.S. and elsewhere in the world about this planetary emergency that we simply have to confront," Gore said.

"I have no plans to be a candidate for president again," he said. "I don't expect to ever be a candidate for president again. I haven't made a so-called Sherman statement, because it just seems unnecessary, kind of odd to do that."