NEW YORK - Sen. Joe Biden spent his first day as an official presidential candidate explaining why he had described Democratic rival Sen. Barack Obama as "clean," and why he had dissed Sen. Hillary Rodham Clinton and John Edwards.

The six-term Delaware lawmaker, who has said for months he'd be a candidate in 2008, formally establish his presidential committee Wednesday and launched a campaign website. It's the second presidential bid for Biden, who pursued the White House in 1988.

But in a conference call with reporters to discuss his candidacy, Biden was peppered with questions about remarks he made to the New York Observer, a weekly newspaper.

In the article, published Wednesday, Biden harshly criticized Clinton and Edwards for their proposals to end the Iraq war. He also questioned the credentials of another leading candidate, first-term Illinois Sen. Barack Obama, while calling him "a mainstream African-American who is articulate and bright and clean."

Biden told reporters that he'd used the word "clean" to describe Obama as "fresh and new," and that the choice of words was not meant to disparage other black candidates who'd run for president in the past, such as civil rights leaders Jesse Jackson and Al Sharpton.

Obama, Biden said, "is probably the most exciting candidate the Democratic or Republican parties have produced since I've been around. He's fresh, new, smart, insightful. Lightning in a jar."

Biden also said he'd called Obama after the controversy surfaced to patch things up.

"He said, 'Joe, I knew what you meant,'" Biden said.

At a Washington news conference earlier in the day, Obama said: "You'd have to ask ... Senator Biden what he was thinking." But an Obama aide confirmed the two senators had indeed spoken.

"Senator Obama said that he didn't take the comment personally," spokesman Tommy Vietor said.

Biden was also grilled about comments he made regarding proposals offered by Clinton and Edwards to stabilize the situation in Iraq.

A 34-year Senate veteran known for his foreign policy expertise, Biden called Clinton's proposal -- which would cap American troops and threatens to cut funding to Iraqi security forces -- "nothing but disaster." He also criticized Edwards, who has proposed immediately removing 40,000-50,000 U.S. troops from Iraq.

"I don't think John Edwards knows what the heck he is talking about," Biden said.

Pressed to explain, Biden reiterated his claim that his rivals' Iraq plans were a mistake. He also said that while the Democratic field has a number of well-qualified contenders, he was the best qualified to serve as president.

"I believe I'm the best prepared of all the candidates," he said. "That I can say someone is qualified but can't take issue with their ideas is a strange phenomenon."

Known for his windy oratory and habit of thinking out loud, Biden's mouth has gotten him into trouble before. Last July, he defended his remark that "you cannot go to a 7-Eleven or a Dunkin' Donuts unless you have a slight Indian accent." Biden said his words had been taken out of context.

And as a candidate for the 1988 Democratic presidential nomination, Biden withdrew from the race in 1987 amid accusations that he had plagiarized passages in a campaign speech from former British Labor Party leader Neil Kinnock.

Asked whether his verbosity would be a handicap on the campaign trail, Biden demurred.

"That's for voters to decide. I don't see it as a problem," he said.

In a video message posted on his new campaign , Biden criticized President Bush's conduct of the Iraq war and warned that his successor would have no margin for error in resolving the conflict.

"This administration's mishandling of the war in Iraq may be the greatest foreign policy disaster of our times," Biden said. "The next president ... is going to have to be prepared to immediately step in and act without hesitation to end our involvement in Iraq."

Biden voted in 2002 to authorize military intervention in Iraq but has since become a vocal critic of the conflict. He's also proposed a plan for peace in Iraq that would divide the country along ethnic lines.

Biden also spoke of a number of domestic challenges he hoped to tackle as president, including health care, boosting job and retirement security, and tackling the threat of global warming.

Biden will transfer US$3 million from his Senate account to his presidential campaign, and said he believed he needed to raise US$20 million total to be competitive in next year's early primaries. Analysts believe Clinton and Obama are likely to raise US$100 million each this year.