John O. Gunn Jr., 50, director of administration and finance at the American Consulting Engineers Council until he went on leave a year ago for reasons of health, died of cancer Thursday at Sibley Memorial Hospital.

Mr. Gunn was a native of Washington and graduate of Wilson High School. He attended Georgetown and Indiana Universities and earned a degree in accounting from Benjamin Franklin University.

He began his career with the welfare fund of the United Mine Workers. About 1960, he joined the National Association of Plumbing-Heating-Cooling Contractors and became comptroller. In 1970, he became comptroller of the National Independent Meat Packers Association. He joined the American Consulting Engineers Council in 1971.

Mr. Gunn was a former senior warden and verstryman at St. Columba's Episcopal Church in Washington and also had sung in the choir. He was a member of the Westbrook Elementary School PTA in Bethesda and was a former treasurer of the Green Acres-Glen Cove Citizens Association in Bethesda. The association serves that part of Chevy Chase where Mr. Gunn lived. He was a member of the Little Falls Swimming Club.

Survivors include his wife, the former Estelle Lessard, and three daughters, Susan, Jeanne and Nancy, all of Chevy Chase.

The family suggests that expressions of sympathy be in the form of contributions to the Organ Fund, St. Columba's Episcopal Church, Washington.