David Samuel Bauer, 65, a professional engineer and more recently an investor and real estate broker in Northern Virginia, died Sept. 8 at Doctors Hospital after an apparent heart attack.

He had his own offices in Rosslyn since 1972.

Born in Greeley, Colo., Mr. Bauer received a degree in mechanical engineering from the University of Colorado.

After working in private industry in Denver, he came to Washington in 1941 as a civilian engineer with Army Ordnance. Five years later, he transferred to the Navy Department as a project engineer.

In 1949, Mr. Bauer entered private industry in St. Louis, Mo. He returned here in 1951, and had his own engineering consulting firm.

In 1956, he gave up his business to work full-time as manager of government relations here for one of his former clients, the Bulova Watch Co. of New York.

When the Bulova Washington office closed in 1959, Mr. Bauer became marketing director for the New York-based firm of Leesona-Moos. He was eastern regional manager here for Nordburg Manufacturers from 1964 until 1972.

Mr. Bauer had been a member of the National Society for Professional Engineers, the American Defense Preparedness Association, the American Society of Naval Architects and Marine Engineers.

A resident of Arlington for 22 years, he had lived in Vienna since 1973.

He is survived by his wife, Charlotte, of the home; two sons, David A. and Stephen W., both of Arlington; two daughters, Christine (Tina), of Alamosa, Colo., and Mrs. V. J. Margretz, of Cedar Rapids, Iowa, and three grandchildren.