Joseph Ezra Roop, 74, retired editor of the Foreign Broadcast Information Service of the Central Intelligence Agency, died of cancer Friday at Fairfax Hospital.

He had joined the information service in 1942 and remained with it when it became a part of the Office of Strategic Services and then the CIA. He retired in 1963.

Born in Johnson County, Mo., Mr. Roop was a graduate of Central Missouri State College. He earned a master's degree in journalism from the University of Missouri and took graduate work in political science at the University of Wisconsin.

He taught journalism at Alabama Polytechnic Institute, now Auburn University. While there, he helped found the Lee County Bulletin, a weekly newspaper in Auburn, and was its editor until selling his share in the paper before coming here.

Mr. Roop was a former president of the Centreville, Va., Citizens Association. He had served on the Fairfax County Planning of Land Use System (PLUS) task force.

He was an avid genealogist and a member of the Roop Society of Carroll County, Md.

He is survived by his wife, Mae, of the home in Centreville; four children, John Englar Roop, of Great Falls, Joseph M., of Arlington, Rachel Roop Beneke, of Centreville, and Mary Shelton Roop Cairns, of Reading, England; two sisters, Louise Cooper, of Warrensburg, Mo., and Mary Swisher, of Windsor, Mo.; two brothers, Alonzo of Oklahoma City, and George, of Canton Okla., and eight grandchildren.