Former vice president Al Gore, who won the popular vote but lost the presidency in 2000, announced last night that he will not seek the White House in 2004, ending two years of disappointment and political exile by saying that another race against President Bush would not be "the right thing for me to do."

"I've decided that I will not be a candidate," Gore said in an interview on CBS's "60 Minutes." "I personally have the energy and the drive and the ambition to make another campaign." But a rematch with Bush, he added, "would inevitably involve a focus on the past that would in some measure distract from the focus on the future that I think all campaigns have to be about."

Gore said his decision not to run in 2004 made it unlikely that he will ever seek the presidency again, but he did not rule out another campaign in the future. "I make this decision in the full awareness that it probably means that I will never have another opportunity to run for president," he said. Others said they did not regard this as the certain end of his political career.

Although some associates recently had begun to think Gore, 54, would not run again, the timing of his announcement caught even close friends and aides by surprise. Gore was finishing a month-long book tour that included an intensive round of media interviews that appeared to signal his political reemergence.

The announcement came the day after an appearance on NBC's "Saturday Night Live," when Gore impersonated incoming Senate Majority Leader Trent Lott (R-Miss.), playing Lott as a southern racist. In other skits, Gore mocked himself and his feelings about losing in 2000 and wistfully pretended to be a decisive wartime president on the set of the popular NBC drama "The West Wing."

Gore offered little insight into what prompted him to stay out of the race or why he announced it last night. The timing of yesterday's announcement was so closely held that Gore's press secretary, Jano Cabrera, was on his way back to Washington yesterday and had to return to New York once he was alerted to the "60 Minutes" interview.

During his recent book tour, Gore had said he would make a decision after the holidays. But he said last night that after spending much of the week in New York with his family, he had come to a decision.

Former president Bill Clinton praised Gore as "the best vice president America ever had" and added that Gore "would have been a fine president, had history taken a different course two years ago."

Democratic National Committee Chairman Terence R. McAuliffe called Gore "a stand-up guy" and said the decision not to run was "courageous." McAuliffe called Gore "a great leader for our party and our country" but said he was not surprised by the announcement because "he had not been reaching out to the people around the country" to lay the foundation for another candidacy.

Throughout the year, Gore sent mixed signals about another campaign. His wife, Tipper, and several of his children had said that they would support another candidacy and that he deserved another attempt at the White House. This fall, Gore attacked Bush's decision to seek approval to go to war with Iraq, denounced the president's economic policies and team and was one of the first Democrats to condemn Lott for his remarks about the 1948 presidential candidacy of Sen. Strom Thurmond (R-S.C.).

A week ago, Gore promised to issue an economic program and details of a new health care program early next year, leading one former adviser to believe Gore was serious about running again.

Friends said they believed Gore was disappointed by the weak sales of the new book, "Joined at the Heart," which he and Tipper just published, along with a photo book about the American family. They also said his fundraising operation had been sluggish and there were no signs that Gore was moving forward energetically on that front. His 2000 network had atrophied.

Gore would have been the front-runner for the Democratic nomination, had he chosen to run. But it was obvious to him and those closest to him that he faced a far more difficult race this time than he did in 2000.

"He hadn't really started to build the bridges with potential supporters," said Iowa Attorney General Tom Miller, who supported Gore's nomination in 2000. "It was getting pretty late. I think it's the right decision."

Gore was finding life as a private citizen both lucrative and enjoyable, according to associates. Besides publishing the books, Gore has been teaching at two colleges in Tennessee, and earlier this year, he joined the investment firm Metropolitan West Financial as vice chairman. He and Tipper just moved into a large home in one of Nashville's wealthiest neighborhoods.

One associate, who had not been tipped about Gore's decision, said he believed Gore's "attitude was: Why should I put up with this? I've got a nice life. I'll help the party, but I don't want to go through this hassle."

Many party insiders blamed Gore personally for losing in 2000 and did not want him to run again, believing the party would be better off with a fresh face. Many of his advisers from the 2000 campaign had decided not to work for him again, and some already had signed on with several of his potential rivals.

Gore alluded to these problems last night. Noting that "the last campaign was an extremely difficult one," he added, "I think that there are a lot of people within the Democratic Party who felt exhausted by that, who felt like, 'Okay, I don't want to go through that again.' And I'm frankly sensitive to that, to that feeling."

In the general election, Gore came agonizingly close to defeating Bush, losing only after a bitter 36-day recount battle in Florida and a Supreme Court decision that closed off his options to continue the recount. After that, he went into political hibernation.

When he began to speak out this fall about Iraq and the economy, Gore showed he still had the capacity to set the tone for his party. "He didn't lack a message the last three or four months," said Donna Brazile, his 2000 campaign manager, "but the machine was in disrepair."

In his "Saturday Night Live" performance, Gore looked like a person who was not thinking about running again, particularly when impersonating Lott. In that role, he said, "I simply meant that things would have been better if Thurmond would have been president because he would have kept white people and black people separate." Playing Lott, Gore also called Thurmond "a genius" who had "wanted to make it illegal for black people and white people to marry each other" and who had "great ideas for raising tax revenue, like making black people pay to vote."

With Gore out of the race, Democrats now face one of the most competitive and wide-open contests for their presidential nomination in decades, with perhaps half a dozen candidates running. None has a prominent national profile.

The most immediate beneficiary is Sen. Joseph I. Lieberman (D-Conn.), Gore's 2000 running mate, who had pledged not to run if Gore did. Sen. John F. Kerry (D-Mass.) and Vermont Gov. Howard Dean (D) already have announced their intention to run. Senate Democratic Leader Thomas A. Daschle (D-S.D.), outgoing House Democratic leader Richard A. Gephardt (D-Mo.) and Sen. John Edwards (D-N.C.) all are actively exploring whether to run. Civil rights activist Al Sharpton also has said he will seek the nomination.

"He had a lot of courage and a lot of class," Dean said. "I feel a certain sense of sadness for him."

In a statement, Kerry said Democrats "owe Al enormous gratitude for years of dedicated and exemplary public service." Edwards, in a statement, said, "Public service is more than a job for Al Gore, it's a way of life."

Gephardt's statement called Gore "one of the most decent public servants I've ever had the privilege to work with" and added that he was "convinced that he would have been a great president." Daschle's statement said, "I respect Al Gore's decision not to seek the presidency in 2004."

A spokesman said Lieberman would not have a statement until today.

There was no official comment from the White House, but a senior Republican official said Gore "wants to keep his position in history as the guy who should've been president" and that "to run again and get trounced would diminish that."

Gore served eight years as Clinton's vice president following eight years as a Tennessee senator and eight years as a member of the House. He ran unsuccessfully for the 1988 Democratic nomination, and he considered running in 1992. Ticking off his trio of eight-year tenures as an elected official, Gore joked last night, "I had another eight-year plan in mind, but it didn't work out."

Staff writer Mike Allen, researcher Brian Faler and special correspondent Michael Zimmerman contributed to this report.

Gore says a rematch with Bush "would inevitably involve a focus on the past."Former vice president Al Gore impersonates Sen. Trent Lott (R-Miss.) on a "Saturday Night Live" parody of MSNBC's "Hardball with Chris Matthews."