Robert H. Barnum, 66, a retired steel company executive and Rear Admiral in the Naval Reserve, drowned Thursday in a creek in front of his home in St. Michaels, Md..

Born in Brooklyn, N.Y., Adm. Barnum was a 1933 graduate of the U.S. Naval Academy. After service on active duty, he entered the Naval Reserve and began a career in business.

From 1939 to 1949, Adm. Barnum served as a general manager and president of William Hunt & Company, an industrial engineering firm, in New York and China, except for four years during World War II which he spent as assistant naval attached at the U.S. Embassy in Santiago, Chile.

In 1949 he joined the U.S. Steel Export Co. as assistant to the president, and from 1950 until his retirement in 1968 served as assistant to the president of the U.S. Steel Corp. in New York.

Adm. Barnum remained in the Naval Reserve and retired with the rank of Rear Admiral. From 1959 to 1965 he held several positions in the Navy League, including the national presidency from 1963 to 1965.

He is survived by his wife, Audrey of the home, and two daughters, Sandra Nygaard of Alameda, Calif., and Patricia Rich of Chappaqua, N.Y., and three grandchildren.