A third-party arbitrator, seeking to end a five-month deadlock over a new contract for Prince George's County's 6,200 teachers, yesterday recommended a slightly shorter work year for the teachers, but said they should forgo a cost-of-living pay increase.

Although a number of the arbitrator's recommendations went in favor of the Prince George's County Educators Association, Paul Pinsky, the president of the teachers' association, said he is "not very pleased with the arbitrator's report, particularly as it concerns the cost-of-living increase."

Pinsky said, however, that the report provides "some basis" on which to continue negotiations. School board chairman Susan B. Bieniasz said the arbitrator's report "looks like a document in which we can begin to find some areas of agreement . . . . I think we can begin to talk again."

The current two-year contract for the county's teachers expires at midnight Aug. 31. The teachers have asked for the new contract to stretch over 10 years, the board over several years but fewer than 10. The arbitrator yesterday recommended a one-year contract.

The teachers' request for a 4.5 percent cost-of-living increase has been the main sticking point in the negotiations, which began last December and broke down in March. The school board offered an across-the-board raise of $382 for next year and said that anything more would force the board to lay off teachers. In his report, the arbitrator noted the school board's proposed budget for 1983-84 of $312 million is already $4.5 million short of what the board needs to maintain current programs.

"It's one thing to be altruistic, it's another to be masochistic," Pinsky said yesterday of the arbitrator's finding that "there are simply no funds upon which the board could reasonably rely" to provide the requested cost-of-living increase.

Seymour Strongin of the American Arbitration Association noted in his report that the county police officers and firefighters have recently settled for no salary increases. In return, their work week will be reduced by two hours.

Strongin recommended shortening the teachers' work year by two days. His recommendations are non-binding and are meant to serve as a departure point for both sides to resume talks.

Pinsky said the 12 members of the association's board of directors would discuss the fact finder's report at a meeting tomorrow night to decide whether continued negotiations are warranted and which recommendations they want to use as a basis for negotiation. Bieniasz said the school board would meet next week.

Strongin also recommended that there be no cutbacks in either tuition reimbursements for teachers who return to school for advanced degrees or in their health insurance coverage. The board had proposed reducing reimbursements and either setting a dollar cap on the teachers' health benefits or reducing the school system's contribution to those benefits.

Pinsky said he was pleased with Strongin's recommendation that a task force be set up to devise procedures for a program in which two teachers can voluntarily agree to share the teaching of a single class. The teachers' association sees this as a way of creating jobs for some 500 teachers who were laid off last year.

Pinsky said if a settlement is not reached by Aug. 31, he will recommend that teachers continue working under the present contract.