Sen. Joseph Lieberman said Tuesday he was caught "completely off guard" by news that Al Gore, his former running mate from 2000, is endorsing Howard Dean for the Democratic nomination for president.

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Lieberman, the moderate Democrat from Connecticut, says he remains grateful to the former vice president for choosing him to run on the presidential ticket in 2000 but still sounded spurned about what will certainly be a huge blow to his campaign for the 2004 nomination.

Asked on NBC's "Today" program whether he felt betrayed by Gore, Lieberman said, "I'm not going to talk about Al Gore's sense of loyalty this morning.

"I was surprised," Lieberman acknowledged in a nationally broadcast interview. "I'm more determined than ever to fight for what I believe is right for my party and my country."

Shown a clip of himself heaping praise on Gore, Lieberman said he'd be "less likely" to say the same things now. As a courtesy to the former vice president, Lieberman delayed entering the 2004 race until Gore made it clear he would not run.

Hours after Lieberman's comments, Gore made his endorsement official, joining Dean in a morning ceremony in Harlem.

Dean thanked Gore for his support, which he said was "announced last night." He called Gore an "extraordinary human being who has taught me quite a bit about foreign policy and defense."

"I'll keep my remarks short. I had no idea we'd have the elected president of the United States here," Dean said, prompting cheers and applause from those in attendance.

Gore said his endorsement was the keeping of a promise he made last December when announcing he wouldn't run for president in 2004.

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Gore Endorses Dean

"I have watched this campaign, and I have listened to all candidates. I think it's a great field," Gore said. "But what I'm about to say doesn't come as a secret or surprise to anybody ... and that is that Howard Dean really is the only candidate who has been able to inspire at the grass roots level all over this country the kind of passion and enthusiasm for democracy and change and transformation of America that we need in this country.

"So, I'm very proud and honored to endorse Howard Dean to be the next president of the United States of America."

Gore defended Dean from criticism about what some say was the wrong stance on the Iraq war.

"Excuse me, but Howard Dean is the only major candidate to make the correct judgment to oppose the Iraq war," Gore said.

An endorsement from Gore, who received more popular votes that President George W. Bush in the 2000 election, likely will firm up Dean's status as Democratic frontrunner.

Five weeks before Iowa's kickoff caucuses, Gore and Dean appeared in Harlem before flying to Cedar Rapids, Iowa, where Dean is locked in a tight race with Rep. Richard Gephardt in the Jan. 19 Democratic caucuses.

Dean would then return from Iowa in time for Tuesday night's Democratic debate in New Hampshire.

Senate Minority Leader Tom Daschle said Gore's endorsement of Howard Dean is a "major prize." Daschle told reporters that Dean "benefits greatly" from the endorsement.

He said it has to enhance Dean's campaign and is further proof Dean is considered by many to be the frontrunner in the race for the Democratic nomination.