He joined the NCC staff in 1960, serving as its executive for religious liberty until 1990. Since then, he bad been the organization's religious liberties counselor. He also had served on the board of the American Civil Liberties Union.
Over the years, Mr. Kelley had filed scores of amicus curiae briefs dealing with religious issues with the U.S. Supreme Court and other judicial bodies. He testified before congressional groups and wrote dozens of articles and more than a half-dozen books.
He championed the rights of such controversial groups as the Branch Davidians, the Church of Scientology and the followers of the Rev. Jim Jones, who died in a mass suicide. He maintained that "one man's cult is another man's religion."
He opposed a constitutional amendment that would permit organized prayer in public schools, doubting the ability of anyone, however well-meaning, to devise prayers that would be meaningful to all while offensive to none.
Two of his major books, "Why Conservative Churches Are Growing" (1972) and "Why Churches Should Not Pay Taxes" (1977), were published by Harper & Row. At the time of his death, he had nearly finished the final editing of a five volume work, "The Law of Church and State in America," to be published by Greenwood Press.
Mr. Kelley, a native of Cheyenne, Wyo., was a 1946 graduate of Denver University. He received a master's degree in theology from Iliff School of Theology. Before joining the National Council of Churches staff, he had been a Methodist minister in Colorado and New York.
Survivors include his wife of 50 years, the former Maryon Hoyle, and a daughter, Lenore Wadsworth, both of West Swanzer; and a grandson.