The retail clerks' union accused the Great Atlantic & Pacific Tea Co. yesterday of violating its union contracts by staffing its new Plus discount food stores with nonunion workers.

A & P laid off more than 100 union members when it closed three local A & P supermarkets this summer, then hired nonunion employes when the stores were reopened this week as Plus units, the union complained.

Thomas McNutt, president of Local 400 of the Retail Stores Employees Union, said yesterday his local has sued A&P in an effort to win back the jobs of the members who were laid off.

McNutt said U.S. District Court Judge Frank Kaufman in Baltimore is expected to rule next week on a union lawsuit seeking to force A&P to submit the dispute to arbitration.

Judge Kaufman rejected a union request to issue a temporary injunction to prevent the three Plus stores from opening with nonunion crews last week, an A&P official said. Executives of the supermarket chain said they would not discuss the dispute while it is before the court.

The three Plus stores in the Washington suburbs are the latest of 14 that have been opened this year by A&P. Patterned after European stores owned by the Tengelmann Group, which purchased control of A&P earlier this year, the Plus stores carry only 800 items priced up to 30 percent below conventional supermarket prices. Customers pick items directly from shipping cartons and must bag or box their own orders.

McNutt said A&P's contract with his union requires the chain to hire union members and pay union wages in any new stores it opens. He claimed the Plus stores are staffed mostly with part-time workers paid less than half the union wage.

A & P contends the Plus stores are not covered by that provision because they are owned by a separate A & P subsidiary, Plus Discount Foods Inc.

If the union lawsuit is successful in forcing A & P to staff the Plus stores with union workers, it could be a major setback for A & P's discount foods experiment. A & P executives have attributed Plus' lower prices to lower operating costs of the stores, apparently including lower wages.