The Air Line Pilots Association late Friday accepted an offer of binding arbitration in its negotiations with Federal Express Corp., putting pressure on the company to accept the offer or face a work stoppage or slowdown in the middle of the busy holiday shipping season.

The National Mediation Board declared an impasse in the negotiations late Thursday, and recommended the binding arbitration to the two sides, which have not been able to reach agreement on a contract since talks started in May, 1994. Federal mediators have been involved since January in the talks, which broke off Oct. 12.Friday afternoon the union's national executive committee for FedEx pilots voted to accept the offer of arbitration, as long as FedEx agrees by 5 p.m. EDT today (Monday), and the terms of the arbitration are agreed to between union and company by next Monday.

If FedEx accepts the offer as well, it would preclude any kind of job action by union or company while the many disagreements are settled. But if the company says no to arbitration, it means a 30-day cooling-off period, after which either side could initiate some kind of job action.

David Webb, a FedEx pilot and spokesman for the union, said the decision was difficult for the union, because arbitration will delayed a final resolution for months. He said the issues will be decided by people not necessarily familiar with air cargo operations such as FedEx. But he said the union believes it has justifications for its bargaining goals and is confident of prevailing.

FedEx spokeswoman Shirlee Clark said earlier Friday the company still is hopeful of a negotiated settlement.

There are risks if the company says no to arbitration. The 30-day cooling- off period would bring renewed negotiations, but uncertainty for shippers, who may be concerned whether the carrier will be able to meet their Christmas season needs. But Ms. Clark would not comment on the possibility of a job action or its effects on shippers.

"We believe the majority of the pilots are as committed as we are to providing excellent service to our customers, and we've been given no indication that they would not continue to serve," she said.

Ms. Clark denied union charges that FedEx is seeking a concession contract.

"We are making a fair and prudent offer of enhancements in pay and benefits," she said. "We are asking for some increased productivity. There certainly are some changes in the work rules needed in order to provide flexibility and make sure we are addressing what we need to do as we operate as a global airline."

The union charges that the changes would require them to work more days to earn the same money, and give the company unreasonable latitude in scheduling.

The pilots are the only union employees at the company. The union started the organizing drive in 1991, and won the vote a year later. But it was not certified to represent FedEx pilots until June 14, 1993. The company fought that certification but lost its appeals in August 1993. ALPA is still trying for its first contract.

FedEx pilots have not received a general pay increase since July 1990. The 2,750 pilots make an average of $100,000 a year, plus overtime, according to Ms. Clark.

If the company says no to arbitration, the union might be able to hurt FedEx without a full strike. Mr. Webb said a work-to-rule job action or a boycott of overtime would clog FedEx's system at the height of its busy season.

"Traditionally, pilots have gone the extra mile, particularly in peak season, which we are in right now," said Mr. Webb. "If everybody did just exactly what they're supposed to do, it (FedEx's reliability) wouldn't happen."

H. Perry Boyle Jr., an analyst with Alex. Brown & Sons in Baltimore, said if FedEx rejects arbitration, shippers probably won't get too concerned until a deadline draws near or threats of job actions are made, although retailers who depend on the carrier for Christmas season deliveries might get nervous sooner.

"The timing is unfortunate," he said.