James Gordon Bennett Mitchell, 69, an architect in the Washington area since 1940 who helped to design commercial, residential and industrial properties, died at the Washington Hospital Center on Saturday of complications resulting from emphysema.

Mr. Mitchell was born in Philadelphia. He studied architecture at the Beaux Arts Institute there and also at Temple University. He came to this area to work for the old War Department. He also worked for the Veterans Administration and the Naval Ordnance Lavoratory at White Oak.

In the late 1950s, he left government and joined the Mariott Corp. as an architect. He worked on the Marriott Twin Bridges motel here. In the early 1960s, he joined Collins-Kronstadt, an architectural firm in Silver Spring. There he took part in a general architectural practice until his retirement in 1974.

Mr. Mitchell, who continued to practice from his home in Burtonsville after his formal retirement, was a member of the Potomac Valley Chapter of the American Institute of Architects. He also was a member of the Burtonsville Lions Club.

Survivors include his wife, Genevieve, of the home; three daughters, Caroline, of the home, Patricia Boltins, of Gambrills, Md., and Joie Morrison, of Silver Spring; a son, Robert I., of Burtonsville, and five grandchildren.