The threat of a hotel strike in the nation's capital ended yesterday when Washington hotel owners and union officials reached tentative agreement on a new three-year contract, following 30 tedious hours of negotiations marked by bitter arguments and a spectacular one-man walkout that caused hotel owners' heads to spin.

Details of the agreement between the Hotel Association of Washington and the Hotel and Restaurant Employees Union Local 25 were scheduled to be disclosed at a union ratification meeting today in the Metropolitan African Methodist Episcopal Church downtown. The hotel association will review the contract Friday, and both sides are expected to ratify the agreement.

Sources involved in the negotiations said that a major provision of the new contract includes a $60-a-week pay increase over the next three years for the average hotel employe -- about two-thirds of what the union originally sought but considerably more than provided for in the last contract reached in 1978.

The increase would raise the average hotel worker's hourly pay about $1.50, from $4.65 to $6.15 over the three-year period. It is expected by both sides to be accepted without a problem, bleary-eyed negotiators said yesterday during a press conference that ended with the customary handshakes and grins.

The package also includes modifications in fringe benefits and some working conditions affecting the 6,000 maids, bartenders, bus boys, waiters, waitresses and cooks represented by the union, which was negotiating with representatives of 24 of the city's major hotels, including the Watergate, Hay-Adams, Madison, Hyatt Regency, Mayflower and the Hilton and Sheraton Hotels.

The negotiations, which began 11 days ago in anger, nearly collapsed three times during the final marathon bargaining session at the Best Western Midtown Motor Inn.

Sources involved in the closed-door sessions said the first serious problem came two hours after Tuesday's midnight strike deadline when the hotel association upped its offer of an $11-a-week salary increase to $46, and the union countered by lowering its initial $96 figure to only $84.

Claiming the union was refusing to bargain seriously, chief hotel negotiator Allen Siegel told federal mediator James R. Williams, "Let 'em strike," the sources said.

Williams quickly returned to the union's side of the second-floor meeting room, and a few minutes of shuttle diplomacy followed. The problem, negotiators determined, was that there were too many negotiators on each team -- about 35 in all. Both sides agreed to pare down their delegations to four representatives each and within a few hours, the $60 raise was agreed upon, the sources said.

That left fringe benefits and some working conditions as the major outstanding issues, and soon even the streamlined negotiating teams were at one another's throats, sources said.

Shortly before 6 a.m., the two sides began yelling at one another. After several minutes, Siegel and Ron Richardson, executive secretary of the union, agreed to apologize.

However, when they rose to shake hands, sources said, Siegel grabbed his chest and fell back into his chair. The 47-year-old attorney, who was hospitalized for five weeks last year with a blood clot in the lungs, was having trouble breathing. Union officials were rushed out of the room, but Siegel declined to call a doctor. Instead, he turned the negotiations over to his young legal partner, Steve Foreman, went to his hotel room and did not return to the negotiating room until late in the afternoon.

The final agreement was announced about 4 p.m., ending a drama that had threatened to tie up some of the city's major hotels at the beginning of a peak convention season at what union leaders contended would be a cost of $1 million a day.

The finale was marked with the same kind of unpredictability that had dominated the two weeks of negotiations, often played out in full view of the news media.

Shortly after noon, Richardson burst from the negotiating room, aides in tow, ran to a van parked in front of the hotel and sped off, leaving stunned hotel representatives wondering if he had gone to launch the strike.

He was upset by the negotiations, he explained later, and had planned to organize an impromptu sit-down demonstration at the International Hotel, which is partially owned by Edward MacMillan, chairman of the hotel negotiating team. But before he reached the hotel, he turned around and came back and apologized for leaving.

A few hours later, the hotel association decided it had negotiated long enough. Its members agreed to a final offer by the union and called the first formal press conference of the final session -- a suprise move that Richardson learned of as he was preparing to go home.

After a few hurried discussions, a joint press conference was held. The heated tempers cooled into smiles. The fighting was over.