The Port Authority and representatives of some of the nation's biggest labor unions remained in marathon meetings well into last night in Washington, D.C., as a Monday deadline looms.

The long meetings fueled speculation that people inside the International AFL-CIO headquarters building were attempting to broker a last-ditch agreement between the authority and Local 85 of the Amalgamated Transit Union, which represents 2,300 bus and trolley workers and low-level supervisors.

So far, those efforts have not succeeded, leaving people who account for 230,000 transit rides a day in Allegheny County wondering whether bus and trolley service will be halted by a work stoppage.

Officials on both sides publicly were saying little.

Authority spokesman Judi McNeil said she last heard from Chief Executive Officer Steve Bland shortly after 9 last night.

"He told me not to anticipate anything groundbreaking to occur for the rest of the night," she said.

Mr. Bland was to remain in Washington today along with the authority's chief negotiator, attorney Mike Palombo, who were expecting to be summoned for a fourth day of meetings.

Patrick McMahon, union president and business agent, and Joseph J. Pass, longtime labor counsel, were representing Local 85 and also were remaining in town.

In a statement released last night, Mr. McMahon said: "We're still here. We've been working practically around the clock since Saturday morning. We are committed to continue to work until we can come up with a fair solution to the situation."

Separate, all-day sessions got under way Saturday morning.

Authority officials yesterday were still covering matters said to be at the heart of the reason why the AFL-CIO and International ATU called them to the capital in the first place. One of the major issues was covering information concerning the authority's continuing financial problems.

Neither side has yet met face-to-face and may not do so because of their sharp disagreements. prompting international union representatives to engage in "shuttle diplomacy."

Mr. Bland and Mr. Palombo have been talking mostly with representatives from the AFL-CIO, exchanging information and answering questions.

The authority board has adopted a "final and best offer" as a contract to be imposed on Local 85 at 12:01 a.m. Monday.

Local 85 has maintained an imposed contract is illegal, would constitute a lockout and would rob members of benefits they've come to expect through past bargaining. If the authority moves ahead with the new contract as it has vowed, union leaders have suggested a work stoppage is likely.

"The last thing we want is to be locked out," Mr. McMahon said last night. "Our members want to keep working through the holiday season, providing consumers with the service they rely on regardless of how long it takes to find a solution."

All of the parties engaged in the highly unusual and unprecedented private talks have a stake in any outcome.

The Port Authority has argued it needs a labor agreement that will reduce long-term health care and retirement obligations, avoid service cuts and satisfy county Executive Dan Onorato's demands to reduce legacy costs in exchange for his releasing $27.7 million in subsidies.

Some observers of the situation speculate the international unions have gotten involved because an imposed contract -- if it stands up in court -- could pose national implications for the AFL-CIO and its affiliates, establishing precedent for private companies and other public entities to do the same as the Port Authority.

The AFL-CIO is a federation of 56 national and international labor unions, including the Amalgamated Transit Union. It represents a total of 10.5 million members.

The Washington meetings came at the last minute, prompting Local 85 to cancel membership meetings that had been scheduled for Sunday. No new meetings have yet to be scheduled.

The eight-member Port Authority board will hold its November monthly meeting tomorrow. The board does not usually meet in December because of the holidays.