Negotiators representing 24 major Washington hotels and representatives of 6,000 hotel workers bargained past an initial midnight deadline into the predawn hours today in an effort to head off a threatened strike at 6 a.m., when the first shift of employes report to work.

It was learned that negotiators for the hotels had increased their wage offer from $32, spread over three years, to $46. The union is seeking $96. The negotiators also had not reached agreement on fringe benefit issues that the union said must be settled to prevent a strike.

Although both sides said they remained hopeful that a strike could be averted, the hotel owners indicated it was up to the union to reduce its wage demand.

Leading members of the Hotel and Restaurant Employees Union Local 25 continued to act as if a strike, the first such walkout in the city since 1946, would occur. This came even though the hotel owners modified their previous pay offer. A special federal labor troubleshooter has joined the talks.

Allen Siegel, chief negotiator for the Hotel Association of Washington, remained optimistic a strike would not occur. "Judging on past history, I don't think there will be a strike," he said. "No one really wants one."

James R. Williams, a federal mediator described by government officials as one of the top three troubleshooters in the nation, was dispatched by the Federal Mediation and Conciliation Service to join the talks, which are being held at the Midtown Motor Inn at 12th and K streets NW.

Williams, who also was involved in 1979 when the Washington Teachers Union struck the public schools for 23 days in March, was requested by Charles Scott, the federal mediator for the Washington area who has been involved in the negotiations since last week.

"The flavor of the meeting was favorable," Williams said during the predinner break. "It's progressing."

The negotiations, which had previously been sidetracked by what one negotiatior termed "posturing" to the media by both sides, settled into hard face-to-face bargaining on major ecnoomic issues.

They include the salary increase, a greater emphasis on seniority, a clause that would keep hotels from reducing any benefits it now gives workers but which are not outlined in the contract and the union's demand that hotels help defray the cost of medical coverage for an employe's family.

Some observers felt that progress on those points would decrease the likelihood of a strike because, the observers said, workers in the union, which has no strike fund, would be less likely to risk economic hardship over noneconomic issues such as arbitration procedures.

But Richardson told a reporter yesterday evening that if he called off the strike only because economic issues appeared resolved, union members would "run me out of town on a rail."

The 24 member hotels involved in the negotiations, which include the Watergate, Madison, Mayflower, Hyatt-Regency and Hilton and Sheraton hotels, have signed a lock-out agreement committing all 24 to lock out their maids, bartenders, waiters, waitresses, busboys, cooks and other union employes if any hotel is picketed.

Local 25, which would have to either borrow money or sell off property to pay any of its members who walked out, has taken that into account in formulating its strike plans.

"We only plan to hit one or two hotels," a union official explained. "That way we will only have to pay strike benefits to a few union members. The ones who are locked out can receive unemployment."

Yesterday morning's negotations began with the hotel association bringing in a special table filled with calculators -- a signal that it finally was ready to begin serious discussions about the union's 36 remaining demands. Before yesterday, both sides had agreed upon only five minor issues.

The hotel association had refused to offer any counter-proposal to the union's demands, but instead concentrated only on the union's request for a $32 per week raise each year for three years.

The association also refused to break its 16-member bargaining committee into small groups for head-to-head talks with the union as has been done in the past, but instead stayed as one bargaining unit -- a move that union officials claim seriously hampered negotiations.

The union's proposed pay increase would total about $32 a week each year over the next three years. That would raise the average hotel worker's hourly wage by 93 cents to $5.58 an hour.

While union officials said they were preparing for a strike, spot checks yesterday with several hotels found few managers who said they had made any special plans for a strike. There were virtually no reports of unexpected cancellations.

"They the negotiators will fiddle until the middle of the night," said R.V. Bryce, manager at the Harrington Hotel, 11th and E streets NW. "I don't think there will be one."

Privately, some hotel owners questioned whether a strike by Local 25 might damage its members, union and Richardson more than local hotels. (Union organizers predicted that the hotel industry and the city could lose as much as $1 million a day in revenues and taxes if there was a strike and the city is entering a peak convention season.) Richardson has never organized such a massive walkout, they said.

The bulk of Richardson's membership earns less than $12,000 a year, excluding tips, the hotel owners said, and while union members have pledged to stay off the job as long as it takes to get a decent contract, by the "second or third week most of those people will really be hurting," a hotel official explained.

Few of the hotel owners and managers doubted yesterday that their union employes would strike if told to by Richardson, especially after Sunday's union pep rally where nearly 2,000 union members chanted strike slogans after the Rev. Jesse Jackson told them that only by being prepared for suffering could they earn more than "slave wages" and retain their dignity.