David E. McCoy, 85, who ended a 40-year career with the Bell System in 1961 as assistant vice president for public relations of four Chesapeake & Potomac Telephone companies here, died of cancer Monday at Sibley Memorial Hospital. He lived in Bethesda.

Mr. McCoy, who was born and reared in Washington, graduated from Dartmouth College in 1918. He served as an officer in the Navy during World War I and joined C&P in 1921.

He began in the firm's commercial department as a clerk and was assistant manager, commercial superintendent and general commercial manager before becoming an assistant vice president for public relations in 1945.

Mr. McCoy was a former general business chairman for the American Red Cross in Washington, a past director of the National Capital Boy Scout Council and a past president of the Dartmouth Club of Washington. He was a member of the Greater Washington Board of Trade, the University Club and the Church of the Little Flower in Bethesda.

Survivors include his wife of 41 years, the former Elizabeth A. Martin, of Bethesda; two children, Dr. Catherine F. McCoy of Southampton, Pa., and Robert M., of Rockville; a sister, Josephine McFarland of Evanston, Ill., and three grandchildren.