Senator Biden of Delaware launched his White House bid with a vivid demonstration of how his loose tongue could liven up the Democratic field, or perhaps drive him out of it altogether.

Mr. Biden ignited a furor with comments he made discussing the appeal of another likely candidate for the Democratic nomination, Senator Obama of Illinois.

“You got the first mainstream African-American who is articulate and bright and clean and a nice-looking guy,” Mr. Biden said in an interview published online yesterday by the New York Observer. “I mean, that’s a storybook, man.”

Mr. Biden’s remarks, and in particular his use of the word “clean,” prompted debate on television news programs and the Internet about his meaning, and whether he was insulting Mr. Obama or other blacks who have run for president.

Mr. Biden said in a conference call with reporters yesterday that he had telephoned Mr. Obama to make sure no offense was taken.

“I called Barack. He said, ‘Joe, you don’t have to explain anything to me.’ … He understood exactly what I meant,” Mr. Biden said. “No one’s going to misunderstand it.”

Mr. Biden said he was alluding to one of his mother’s favorite compliments, “Clean as a whistle; sharp as a tack,” in describing Mr. Obama’s novelty on the political scene.

As he explained himself yesterday, the Delaware senator became almost bizarrely effusive about his colleague from Illinois.

“This guy is a superstar. … He is probably the most exciting candidate this party has had in a long time,” Mr. Biden said. “This is a guy who absolutely touched a nerve and the imagination of the people of this country in a way I’ve not seen anybody before do. … This is a very special guy. This is like catching lightning in a jar.”

Mr. Biden spoke of Mr. Obama so glowingly that reporters wondered aloud why Mr. Biden was not inclined to give up his presidential ambitions and throw his weight behind Mr. Obama.

“I think he’s great. I think they’re all great. I think I’m better. I think I’m more prepared,” Mr. Biden said.

In a statement, Mr. Obama said he was not offended by Mr. Biden’s remarks but did not consider them well-informed.

“I didn’t take Senator Biden’s comments personally, but obviously they were historically inaccurate,” Mr. Obama said. “African-American presidential candidates like Jesse Jackson, Shirley Chisholm, Carol Moseley Braun and Al Sharpton gave a voice to many important issues through their campaigns, and no one would call them inarticulate.”

While debate on the Web focused on Mr. Biden’s use of the word “clean,” one black columnist and commentator said the Delaware senator’s description of Mr. Obama as “articulate” could rankle many blacks.

“Of course, it’s offensive,” the executive editor of the Chicago Defender, Roland Martin, said. “White people need to stop with this ‘articulate’ nonsense. I am sick and tired of individuals coming across an African-American and saying, ‘Oh, my goodness, you’re so articulate.’ … You never see that kind of statement made about white candidates.”

Mr. Martin, who hosts a radio program, said he expects Mr. Biden to take some heat from black voters. “I can guarantee you Biden is going to get lit up like Christmas,” the commentator said.

The new flap over Mr. Biden’s remarks was a stark reminder of how his candid speaking style could be a liability as he runs for president. During a visit to New Hampshire last year, he triggered a similar controversy when he said, “You cannot go into a 7–11 or a Dunkin’ Donuts unless you have a slight Indian accent.” The senator said he was paying tribute to the growing success of middle-class Indian-Americans in his home state.

Still, Mr. Biden’s unvarnished style could be an asset. At a time when most of his opponents for the nomination appear reluctant to engage in the rough-and-tumble exchanges typical of a presidential race, he is willing to take the other candidates on, by name.

After telling reporters that Senator Clinton is clearly “qualified” to be president, Mr. Biden attacked as unrealistic her proposals on Iraq. “Her ideas are incorrect for how to proceed in Iraq. I do not understand how it makes sense for us to say that the way to deal with the Maliki government, if it does not respond, is to essentially stop training their troops or supporting making them viable,” the Senate Foreign Relations Committee chairman said.