WASHINGTON - Former U.S. Vice President Al Gore's surprise announcement that he would not challenge President Bush in the 2004 presidential elections has thrown the field wide open for Democratic presidential hopefuls.

Gore was expected to explain further his decision at a news conference on Monday afternoon, in Raleigh, North Carolina, the latest stop on his book tour.

"I think that a campaign that would be a rematch between myself and President Bush would inevitably involve a focus on the past that would, in some measure, distract from the focus on the future," Gore said in an interview on CBS' "60 Minutes."

The announcement ended months of speculation over a possible political rematch between Gore and Bush, who narrowly defeated the former senator from Tennessee in the 2000 presidential election.

"The last campaign was an extremely difficult one, and while I have the energy and the drive to go out there and do it again, I think that there are a lot of people within the Democratic Party who felt exhausted by that," Gore said.

The biggest beneficiary of Gore's decision to step aside is his former 2000 vice presidential running mate, Sen. Joseph Lieberman of Connecticut.

The senator said in a statement on Monday he would announce next month if he is to run or not.

"Obviously, in light of Al's announcement I will spend time over the coming holidays talking with my family and friends, and announce my decision about a campaign for the presidency in early January," he said.

Lieberman began exploring prospects for a possible 2004 White House bid shortly after a divided Supreme Court effectively decided the 2000 race for Bush by refusing to permit Gore a recount in Florida. Though Gore won the popular vote, he lost to Bush after the bitter 36-day recount battle.

Lieberman had said if Gore ran again, he would step aside.

DOOR OPEN FOR OTHER DEMOCRATS

While Gore's decision clears the way for Lieberman, it will also likely open the door to other potential candidates to jump into what will be a wide open contest.

"This helps any and all Democrats considering running because Al clearly would have been the front-runner. Polls showed that," said a former senior adviser in the 2000 Gore-Lieberman campaign. "Now it is wide open."

Rep. Richard Gephardt of Missouri, who stepped down as House of Representatives minority leader last month, has also raised speculation he would run. And Gore's decision may also nudge into the race Senate Democratic leader Tom Daschle, who has long considered a bid.

"This will put more pressure on Daschle and Gephardt," a former Gore adviser said. "In recent months, it has been Al taking the lead in responding to Bush's economy, war ... Now people will be turning more to see what Daschle and Gephardt have to say."

Daschle and Gephardt, in separate statements, saluted Gore as a trailblazer and dedicated public servant. "Al Gore won the popular vote in 2000 and I am convinced he would have been a great president," Gephardt said. "Our nation would have benefited from his leadership over the past two years and the Democratic primary process will lose a strong voice and accomplished leader without his participation."

Daschle said he respected Gore's decision and looked "forward to his continued leadership and ideas for our party and for America."

Other possible Democratic presidential contenders include Sen. John Kerry of Massachusetts, Sen. John Edwards of North Carolina and Vermont Gov. Howard Dean.

Dean told CNN Gore's decision would help the party.

"It certainly does open up the party for new ideas that actually make sense and I think, perhaps, take the Democratic Party in a different direction than its been going," Dean said.

A former member of the House, a former senator and the son of a senator, Gore was vice president for eight years under former President Bill Clinton and became one of his closest confidants.

Gore made a series of public appearances in recent months that raised expectations he would run for president again. Last month, Gore saturated the media, promoting a book written with his wife, Tipper, and on Saturday was the host of TV comedy show "Saturday Night Live."

Gore told "60 Minutes" he had made the decision not to seek the presidency fully aware that 2004 would probably be the last opportunity he would ever have to run for president, but said he was not retreating from public life.

"I intend to remain actively involved in politics, " Gore said. "I want to help whoever the Democratic Party's nominee is in 2004 to win the election."