Bill Bradley's furious effort to lobby leaders of organized labor has cast doubt on what had been the near-certain AFL-CIO endorsement of Vice President Gore's presidential bid next week.

Bradley, boosted by the success of his campaign, has persuaded leaders of some of the biggest unions in the AFL-CIO to press for a delay of the endorsement.

These dissenting unions do not have enough votes to block an endorsement, according to numerous sources in labor, but they are influential enough to give AFL-CIO President John J. Sweeney serious pause as he decides whether to press the matter on Oct. 14.

The odds remain in Gore's favor and a solid majority of the 68 member unions in the labor federation are prepared to back his bid for the Democratic nomination, some very strongly, according to these sources.

"We are going through the process," said Sweeney, who wants to endorse Gore but wants it to be as much of a consensus decision as possible. "I hear very, very few who are pushing for Senator Bradley," he said, adding, however, "there are some people who think we should take a little longer."

For the five days leading up to Oct. 14, when Sweeney has to decide whether to bring up the endorsement, union leaders will meet every morning to hash through the dispute.

The dilemma for Sweeney and other Gore backers is that they know that a postponement of the decision to endorse would be viewed as a major blow to Gore. At the same time, pushing an endorsement through over objections of key unions would be, in the words of one union leader, "a paper endorsement," lacking the enthusiasm to be meaningful.

While acknowledging the union endorsement at this time would be a major boost to a campaign that has suffered a number of setbacks lately, Gore officials note that even if the AFL-CIO does not come through next week, Gore has received the backing of many national unions and their local affiliates. The state branches of the United Auto Workers and the American Federation of State, County and Municipal Employees, have, for example, endorsed Gore.

Both Gore and Bradley have been aggressively lobbying labor. Last week, top officials of both campaigns met separately for one-hour sessions with union leaders here at the Hay-Adams Hotel. The purpose of the sessions was to present each campaign's strategy to win the nomination as well as the general election.

Bradley has been concentrating heavily on the unions so far holding out from an endorsement, including the Teamsters, the Service Employees International Union (SEIU), the United Food and Commercial Workers and the UAW.

The Teamsters, a wild card within the AFL-CIO under the new leadership of James Hoffa, is "operating from the philosophy that it is too early to endorse," said Chip Roth, Teamster spokesman. Teamster leaders have been friendly to Bradley, noting that he attended a meeting of the public employees branch, spoke by conference call to the executive board and has talked to Hoffa a half dozen times. In addition, they cite Bradley's willingness to postpone opening the border to Mexican trucks, as is called for under the North American Free Trade Agreement.

The Food and Commercial Workers have strong ties to the Teamsters, on whom they depend to support strikes at supermarkets during wage and organizing disputes. The UAW has been deeply angered over the administration's free-trade policies and does not want to take a step that would be seen as supporting those policies.

One of the major battles for Gore and Bradley has been over the support of the SEIU, a key union with the largest number of members of any union in such crucial primary states as California, New York and New Hampshire. When Bradley and Gore last week addressed a major Northern California SEIU local of health workers, they used some of the strongest language of the campaign.

"I've never been tempted to turn my back on the Democratic Party," Gore said, referring to Bradley's brief flirtation with an independent presidential candidacy in 1996. "I've never been tempted to . . . divide the progressive coalition."

Bradley shot back that he is a better general election candidate than Gore. "The objective of nominating somebody is to win in the fall," Bradley said. "People have come up to me, in hotels and restaurants, and said, 'I'm an independent or a Republican and I would vote for you, and I would never vote for him.' "

The union local voted to support Gore.

Staff writer Frank Swoboda contributed to this report.