They had to duck out of Pittsburgh for four days of secretive talks to do it, but representatives of the Port Authority and its union reached a settlement that came as both a relief and surprise to commuters braced for the worst.

Special diplomacy in Washington, D.C., by national officials who oversee the local bus drivers union was a major factor in reaching the agreement last week. Local talks between the transit agency's representatives and leaders of Local 85 of the Amalgamated Transit Union had been stalemated for months.

The next step likely will take place next Sunday, when Local 85 officials plan to explain the tentative agreement to their 2,300 members and to take a ratification vote. If rank-and-file members approve the agreement, the Port Authority board will call a special meeting a few days later to hold its own vote.

The tentative settlement reached on Tuesday night came less than a week before the Port Authority intended to impose new contract conditions on workers unilaterally tomorrow.

The union, which represents bus-trolley operators, mechanics, other hourly personnel and low-level supervisors, had not announced how it would react to that. But a walkout affecting the people who depend on it for 230,000 rides a day was clearly possible.

The last local transit strike occurred in 1992.

Both sides have declined to provide details of the agreement until it goes before those who will actually vote on its approval. Local 85 employees are to continue working under terms of the previous contract that expired June 30 until board and union approval take place.

The AFL-CIO and the International ATU were perceived as key parties in moving the negotiations forward, in unprecedented fashion. Their officials may have been concerned that if the Port Authority's unilateral contract stood up to a court challenge, it would be harmful to union efforts to achieve strong contracts elsewhere in the country.

The president of the International ATU is Warren S. George, a former Port Authority employee and Local 85 official who was credited with helping to bring the feuding parties to Washington. There, negotiations could take place in a calmer atmosphere than under media scrutiny and public pressure in Pittsburgh, said International ATU spokesman Shawn Perry.

"Everybody was tired of seeing the contract negotiated in the press" and on talk radio, he said.

Local 85 had maintained that an imposed contract would be illegal, robbing members of benefits they've come to expect through past bargaining.

Port Authority officials, however, maintained they needed a labor agreement that would reduce long-term health care and retirement obligations. County Executive Dan Onorato had insisted that such costs be brought under control before he would release $27.7 million in subsidies to assist the agency.

"I am pleased to hear that leaders [of the union and authority] have reached a tentative contract agreement and that transit will continue without interruption," Mr. Onorato said after the settlement was announced.

Some organizations and businesses in the county had spent months preparing for a strike possibility, remembering the disruptions created by the 28-day walkout that ended through a court order 16 years ago.

More organized car-pooling and flexible work schedules were among the alternatives being explored, apparently to be filed away until the next serious contract dispute arises.