Four Northern Virginia architectural firms have received design awards in a competition sponsored by the Virignia Society of the American Institute of Arechitects. James W. Ritter of Springfield won for a design of an artist's studio in Waterford, Va.; the VVKR Partnership of Alexandria for a design of a two-story British Aeroservices Inc. building at Dulles Aiport; Dewberry, Nealon and Davis and the Joseph Boggs Studio were cited for the remodeling of a hip-roof ranch house on seven acres in the lorton area, and Ward & Hall & associates won for the design of the Crescent Plaza office building in Falls Church.

The 354 tenants of two adjacent apartment buildings in Foggy Bottom have been notified that the new owners, John Mason and Stuart Bernstein, plan to convert the 1960-vintage structures to cooperative ownership early next year. The properties, at 940-50 25th St. NW, were purchased from investor-developer John H. Safer for slightly more than $8 million. The units are expected to be priced at about $60 a square foot, Mason said.

The newly renovated Professional Centre building at 5001 Silver Hill Rd., Suitland, has been reopened by International Realty Consultants Inc., which bought the structure in August from Monumental Life Insurance Co. The insurance company provided $250,000 in financing for the renovation. The three-story former medical office building has been converted to commercial office space.

Digital Equipment Corp., a major producer of mini-computers, has broken ground in Lanham for a 63,000-square-foot building to house area facilities. The site is near the intersection of Rte. 50 and the Beltway. Edward M. Crough Inc of Rockville is the general contractor; Donald N. Coupard Associates designed the two-story building.

Construction has begun on Park Washington, the first town house-style cluster of office buildings in Falls Church. Scott, Long & Foster of Oakton is building the $1.9 million complex. It was designed by architects Paul Barkley and Harold Pierce, who also head the development group. The condominium project includes the restoration of the historic O'Banonon house, which is part of the planned cluster on North Washington Street. The project is expected to be completed next fall.