Ralph C. Northrop, 74, retired real estate official with the Post Office Department and a resident of the Washington area for more than 55 years, died at Fairfax Hospital June 9 of a cardiovascular ailment. He had been hospitalized for gall bladder surgery.

Mr. Northrop, who was born in Farnhamville, Iowa, moved to the Washington area in 1925. He took a job with the Treasury Department and later transferred to the Post Office Department, where he specialized in real estate. He retired in 1964.

A former resident of Arlington, Mr. Northrop was a member of Clarendon Presbyterian Church there. He was living in Falls Church at the time of his death and belonged to Idylwood Presbyterian Church there.

Survivors include his wife, the former Clara Peters, whom he married in 1929, of Falls Church; one son, Ralph C. Jr., of Kensington; three daughters, Maxine Richmond of St. Cloud, Minn., Donna Wiuff of San Mateo, Calif., and Dolores Huffman of Roanoke, Va.; one sister, Ruth Mills of Marion, Iowa; three brothers, Paul, of Fountain City, Wis., George, of Tombstone, Ariz., and Lisle, of Forest Park, Ill., and eight grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Memorial Fund, Idylwood Prebyterian Church, Falls Church.