Last July 28, Marvin Goldman, president of the K-B Theatres chain, called in his secretary Evelyn Jayson and dictated a brief letter.

"Dear Leonard," he wrote Leonard Sanford, business agent for Motion Picture Machine Operators Local 224, "according to the provisions of the existing contract, K-B Theatres and its affiliates desires to terminate the contract between itself and Local 224.

The letter was typed, Goldman signed it, and Jayson addressed the envelope and tossed it onto the out box. Usually a receptionist left the office early enough to drop the letter into a mail box across the street in time for the 5 p.m. pickup.

What happened to the letter to Sanford, however, isn't known. The Union leader says he never got it. And as a result, the theatre chain lost an unfair labor practices charge it had filed against the projectionists' union.

K-B had accused the union of failing to bargain for a new contract. Administrative law judge Herbert Silberman ruled, however, that the union had no need to bargain, because it already had a valid contract.

The critical question, Silberman said, was whether the company had properly notified the union that it was terminating the old contract rather than allowing it to automatically extend for another year.

Despite the testimony of Goldman and his secretary that the letter had been typed and handled in the usual way, Silberman ruled that the company failed to give the union proper notice of the contract termination.

"No mitigatin circumstances can be spelled out from such careless handling of a letter whose prompt delivery presumably was of importance to the company," said the judge.

Goldman was out of town yesterday and could not be reached for comment on the decision.