Robert C. Heeney Sr., 58, a criminal trail lawyer and senior partner in the Rockville law firm of Heeney, Armstrong and Heeney, died of cancer Monday at Georgetown University Hospital.

A former assistant state's attorney in Montgomery County, he was an architect of Montgomery County's Public Defender System.

Mr. Heenry tried more than 100 capital cases during his career, including the widely publicized Giles-Johnson rape death-penalty case in the early 1960s. He also led the successful defense team in the trial of Indian militants who had occupied the historic reservation village of Wounded Knee, S.D., for 70 days in 1973.

In 1968, his petition to suppress wiretap evidence obtained by tapping the phones of his clients' employer led to a ruling that Maryland's law on wiretap evidence was unconstitutional.

Mr. Heeney was born in Newark, N.J. He graduated from Georgetown University's Foreign Service and law schools after serving in the Army Signal Corps in Africa in World War II.

He was a Fellow of the American College of Trial Lawyers, a founder, director and past president of the National Association of Criminal Defense Lawyers, a former president of the Montgomery County Bar Association and a former vice president of the Maryland State Bar Association. He served on the Maryland Governor's Committee on Revision of the Criminal Law.

Mr. Heeney, who lived in Gaithersburg, was a former president of the Oakview Citizens Association in Silver Spring. He served for many years as a volunteer firefighter with the Laytonsville Volunteer Fire Department and coached baseball and basketball teams for neighborhood youngsters. He was a member of St. Peter's Catholic Church in Olney.

Survivors include his wife, Marjorie, of Gaitherburg; two sons, Thomas L., of Damascus, and Robert C. Jr., of Annapolis; three daughters, Patricia M., of Denver, Elizabeth A. Winslow of Atlanta, and Margaret Rose, of Leonardtown, Md.; two sisters, Margaret R. Shaw of Little Falls, N.J., and Rosemary Mahon of Allenhurst, N.J., and a brother, John, of Bloomfield, N.J.