WASHINGTON (AP) -- Former Vice President Al Gore has decided not to run for president in 2004, a senior Gore adviser said Sunday.

Gore planned to make the announcement on CBS 60 Minutes, the adviser said.

Gore would have been the likely front-runner in the Democratic field, even though many party activists have said privately they hoped he wouldn't run.

After gradually re-entering politics over the last year, the Democrats' 2000 nominee campaigned for selected candidates around the country this year, then spent the last month promoting a book on the family that he wrote with wife Tipper and making an extensive round of media appearances, including Saturday Night Live this weekend.

Gore's decision opens up the 2004 presidential field for Democrats. Vermont Gov. Howard Dean is running and Massachusetts Sen. John Kerry has formed an exploratory committee and will announce his decision after the new year. Connecticut Sen. Joe Lieberman, Gore's running mate in 2000, has said he is interested in running

Also considering a run are Senate Democratic leader Tom Daschle, Missouri Rep. Dick Gephardt and North Carolina Sen. John Edwards.

Since re-entering the public arena, Gore has been talking about his views on issues from Iraq to health care to the economy and sending mixed signals on whether he planned to run.

Some aides said the 54-year-old Gore would feel differently from day to day about the decision. He had said he planned to deliberate through the holidays and announce a decision after Christmas.

But Gore finished a round of media appearances Saturday night and decided to go ahead with the announcement. Aides did not immediately say why he changed his timetable.

A year ago, Gore accepted the job of vice chairman of a Los Angeles-based financial services holding company, Metropolitan West Financial. The former vice president is helping the firm find investments overseas as well as private-equity investments in biotechnology and information technology.

For the last year, he has been juggling that job with his duties as college professor, guest speaker and author of the book about the American family. He had been traveling between New York, Los Angeles, Washington, his teaching jobs in Tennessee and his new home in the suburbs of Nashville.

Many Democratic activists had voiced opposition to Gore running, citing the fumbled opportunities of the 2000 campaign when Gore had the advantages of incumbency and a booming economy. Gore lost the presidency to George W. Bush after an extensive recount in Florida came up short by just over 500 votes.

Gore disappeared from public view for almost a year after the election, saying that President 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, 2001 terrorist attacks on the World Trade Center and the Pentagon drastically changed the political climate.