A union local said yesterday it had filed charges of unfair labor practices against American University on behalf of 94 cleaning-service employes who the union contends were dismissed for trying to unionize.

The charges were filed with the National Labor Relations Board by the Hotel and Restaurant Employees Union Local 25, which will ask that the employes be reinstated, union officials said.

Employes also may demonstrate at the university on Friday, their last day on the job, workers and union officials said, and they may picket.

American University sent its 94 cleaning employes a letter last week telling them they would be out of work as of Jan. 7 and that thereafter, their work would be contracted out to a cleaning company.

University officials said it was a budget-cutting move, saving an estimated $250,000 a year at the financially squeezed institution, and that union activities had nothing to do with the decision.

"The changeover had been considered since last spring . . . and nothing significant had occurred" in the way of union activity by then, said Marion Martin, a university spokeswoman.

No one at the university had received official notification of the NLRB filing by late yesterday and therefore could not comment on it, Martin said.

Union officials said organizing efforts started in October and that signs of increasing support among employes prompted the firings. "They wanted to get out from under this unionizing , and one of the ways out of it is to subcontract," said Ronald Richardson, secretary-treasurer of Local 25.

About 104 cafeteria workers at the university already are under a union contract with a no-strike clause, Local 25 officials said. If the cleaning employes picket, the cafeteria workers would have to decide whether to cross the picket line.

Neither the Washington office nor the Baltimore regional office of the NLRB could confirm yesterday that the charges had been filed, but spokesmen said the papers may be on the way to Baltimore.

The university's letter to the cleaning employes said the university would try to help them get jobs at the new cleaning service, Unified Services Inc., or elsewhere.

But the employes say this would mean a substantial cut in pay and benefits for most of them. As university employes, they and union officials say, they earn between $3.75 and $6 an hour with paid annual leave based on length of service and a retirement plan.

At Unified, the wages are $4 an hour, and there is no retirement plan, said Unified President Jerry Davis Jr., and the employes would have to start over earning vacation time. About 65 new employes are needed to fulfil the $800,000-a-year contract at the university, Davis said.