Safeway Stores Inc. broke ground Saturday morning for a $3 million supermarket in downtown Silver Spring that will cost more than $50 a square foot to construct -- the highest cost of any Safeway in the United States. The average cost per square foot for Safeways is $27.

About 25 persons representing Safeway, which is the nation's largest supermarket chain, and various municipal and civic groups watched as a few shovelsful of earth were turned over by Don Smith, the company's Washington division manager, and Tim Minard, project director of the Silver Spring Revitalization Design Group.

They stood in the middle of a paved parking lot at Fenton and Thayer Avenues; behind them was the existing Safeway, at 29 years one of the 10 or 15 oldest of Safeway's 163 area stores.

The new Safeway is scheduled to open May 24, 1981. It will have indoor parking, and a delicatessen, bakery and pharmacy. Members of the East Silver Spring Civic Association requested the latter because the existing store has no specialty departments.

Safeway also is constructing replacement supermarkets in Georgetown and in Northwest D.C. There the old stores are being kept open until the new ones are ready, but the small size of the Silver Spring site necessitates demolition of the existing store first to expand parking facilities beneath the new store. It was closed the previous Saturday, and the 40-plus employes were transferred to other Safeways.

A sign at the entrance to the old store says Safeway is running buses to its store on Georgia Avenue near the Beltway. A nearby Safeway is on University Blvd. near Colesville Road.

Safeway officials said a resurgence in downtown Silver Spring caused partly by the nearby Metrorail station was one reason they decided to build a bigger store.