Joseph Cobourn Hummer, 72, a retired automotic accountant who had been the choir director at several churches in the Washington area, died of cancer Friday at the Circle Terrace Hospital in Alexandria.

Mr. Hummer was born in the Georgetown section of Washington and attened the Stewart Business School in Washington.

He began his career in 1929 with the old Sterrette Operating Service, a supplier of parts for General Motors trucks. In 1940, he joined the Paul Brothers automobile distributorship in Washington. About 1945, he went to work for the Cherner Motor Co., a Ford dealership in Washington, and remained there until the business closedin 1973. He then worked for Jerry's Ford in Annandale until 1979,when he stopped working for reasons of health.

A lifelong Episcopalian, Mr. Hummer began directing church choirs when he was still in high school. He began at St. Paul's Episcopal Church at Bailey's Crossroads. Over the years, he also directed the choirs at Trinity Episcopal Church in Manassas, St. Clement's Episcopal Church in Alexandria and Grace Episcopal Church in Alexandria.

Mr. Hummer also was a member of the Anglo-Catholic Union, a church organization. At the time of his death, he was a member of the Ascension and St. Agnes Episcopal Church in Washington. He had restored a number of pieces of church art while at Grace Church in Alexandria.

Surivors include his wife, the former Elizabeth L. Marsteller, of Alexandria, where Mr. Hummer lived, and a sister, Frances Hummer, of Arlington.