Updated

Calling it the "most difficult decision I have ever made," former Vice President Al Gore said Monday that he decided during rehearsal for his hosting job on Saturday Night Live last week not to run for president in 2004.

"I wish I could tell you that right in the middle of the rehearsal of one of those comedy skits, it just hit me like that, but that's not the way it happened. It was just a slow dawning of what I felt was the right thing to do," Gore said during a press conference in Raleigh, N.C., where he was plugging his book Joined at the Heart, co-authored with his wife, Tipper.

"I determined that I might as well go ahead and make the decision sooner rather than later, at least in the middle of December instead of the first of January. But I didn't make the decision really until Friday morning," he said.

Gore, who came agonizingly close to winning the presidency two years ago, announced Sunday that he will not run again in two years. He said he feared that a 2004 rematch with President Bush could degenerate into a grudge match.

"My reasons ... didn't come down to any single factor, but because I have run for president twice before and because a race this time around would have focused on a Bush-Gore rematch, I felt that the focus of that race would inevitably have been more on the past than it should have been when all races ought to be focused on the future," he said on Monday.

Gore said that he probably will not have another opportunity to seek the White House and that he is "completely at peace with the decision."

In fact, Gore seemed very at ease during the press conference, throwing out frequent jokes, telling one reporter not to break out the "chisel and granite" to write his political epitaph just yet, and responding to a question about his favorite skit during his Saturday Night Live gig, a recreation of the extended canoodle he and Tipper participated in on the podium at the Democratic National Convention the night he accepted the Democratic nomination.

"My favorite part of Saturday Night Live, the kiss. And I want you all to know that was real, that wasn't fake," he said laughing.

Gore won the popular vote by half a million votes in 2000, but conceded to Republican Bush after a tumultuous 36-day recount in Florida and a 5-4 Supreme Court vote against him. Gore's concession came Dec. 13, 2000, just over two years ago.

Gore said the first person he called about his decision was CBS' 60 Minutes anchor Lesley Stahl.

During their interview, he told Stahl that while he still had the energy and drive to run again, "there are a lot of people within the Democratic Party who felt exhausted [by the 2000 race] ... who felt like, OK, 'I don't want to go through that again.' And I'm frankly sensitive to that feeling."

Gore's departure from the playing field leaves the Democratic nomination wide open.

Some Democrats, including Gore's 2000 running mate, Sen. Joe Lieberman, were among the first to thank Gore for his public service before launching into plans about their own futures.

"What was until yesterday only a possibility, an abstraction, this morning becomes a reality, a concrete reality, and it is an awesome opportunity, one to be taken with the greatest of seriousness," the Connecticut Democrat told reporters Monday. "As I have said to many of you when you asked me how likely was it that I would run if Al Gore did not run, I said I probably would run if Al Gore doesn't run, and that remains the case."

Lieberman, who sponsored the Senate resolution on Iraq demanding disarmament, said he will think about his decision while on a scheduled trip to the Persian Gulf, where he is headed this week to meet with U.S. soldiers and pass along holiday greetings from family at home.

An outgoing Senate Governmental Affairs Committee chairman and orthodox Jew, Lieberman was said to have been consulting with religious authorities about ways to renege on the pledge not to run if Gore did. On Monday, he said that while a decision was not definite, he could now seriously consider a bid.

"He gave me the extraordinary opportunity to be his running mate in 2000. I can never thank Al and Tipper enough," Lieberman said. "I intend in the next weeks to speak with my family, friends and supporters and then to announce — make a decision and announce — in early January, but for now I wish to thank Al Gore for his leadership, his service and the opportunity he gave me to run in 2000 which makes it possible for me now to make this decision."

On Monday, Sen. John Kerry, D-Mass., said that Gore's decision was never a factor in his plans. Kerry formed an exploratory committee earlier this month.

"I'm on the same schedule I was on," Kerry said. "I've been on a track to organize a national campaign. I think that is going very well. I'm extraordinarily encouraged by the support I've been getting. And I intend to continue to do it with the same intensity and the same focus that I've applied to it up until now."

Among other Democrats, Vermont Gov. Howard Dean already is running. Also considering the race are Senate Democratic leader Tom Daschle of South Dakota, Missouri Rep. Dick Gephardt and North Carolina Sen. John Edwards. Those close to Gephardt have said he was "very, very likely to run" no matter what Gore decided.

Gore said Monday that he hadn't decided whether to endorse any candidate.

"I haven't ruled anyone in and anyone out. I probably will endorse someone, I don't know for sure, but I probably will, and I have communicated directly with Sen. Edwards and Sen. Lieberman and Sen. Kerry. Each one has asked for my support," he said.

Gore said he thought the economy would be the primary issue in the 2004 race, noting that Bush's father had a soaring approval rating in the polls but then stumbled and lost in 1992 because of the sour economy. But he added, he couldn't say for sure what the public will focus on in 2004.

"Anybody who says they can predict what is going to happen two years from now is not being realistic," he said, later adding that it's premature to write his political epitaph because he still plans to remain actively involved.

Bush, whose approval rates are in the 60s, had almost a 20-point lead over Gore in polls that pose a rematch, with an even bigger lead over other Democrats. Gore and Bush were running even before the terrorist attacks of Sept. 11, 2001.

Party activists were critical of Gore for losing despite a booming economy and eight years of a Democratic administration. Gore even lost his home state of Tennessee; a victory there would have given him the White House.

After gradually re-entering politics over the past year, Gore campaigned for selected candidates this year, made trips to Iowa and New Hampshire, then spent the last month promoting the book.

A year ago, Gore accepted the job of vice chairman of Metropolitan West Financial, a Los Angeles-based financial services holding company. He has been juggling that job with his duties as college professor, guest speaker and author.

Gore ran for president unsuccessfully in 1988 and then, while a Tennessee senator, was surprised to be picked as Bill Clinton's running mate in 1992. Though Gore often was criticized as overly controlled and cautious, he was praised for the work he did as an influential vice president.

He used his expertise in science and technology to be the White House point man on telecommunications reform and the information superhighway.

Clinton said Sunday night: "Al Gore was the best vice president America ever had. He would have been a fine president had history taken a different course two years ago.

Gore disappeared from public view for almost a year after the 2000 election, saying Bush deserved a chance to begin his presidency without continued criticism from his election opponent. Just as Gore was beginning to re-emerge politically, the Sept. 11 attacks altered the political climate.

The Associated Press contributed to this report.