Spotswood I. Quinby, 54, a residential builder in Montgomery County from the 1940s to the mid-1960s and a real estate salesman for the last 15 years, died of cancer Friday at his home in Rockville.

At the time of his death, Mr. Quinby was vice president in charge of the commercial development division of the Chris Coile Corporation, a subsidiary of Merrill Lynch Realty, in Bethesda.

He had spent 10 years as a real estate salesman with Shannon & Luchs and then about four years with Montgomery Realty in Bethesda before joining Chris Coile.

Mr. Quinby had been president of the National Exchange Club and was a life member of the Washington Board of Realtors' Million Dollar Club.

He was born in California and had lived in this area since the mid-1940s. He attended the University of Virginia.

Survivors include his wife, Ginette N., of Rockville; a son, Spotswood I. Jr., of Bethesda; two daughters, Karen Jennings of California and Kathy Gargiulo of Columbia; a stepson, Nick Baker of Gaithersburg; his father, retired Navy Capt. C. Spotswood Quinby of Englewood, Fla., and five grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the American Cancer Society.