F. Harper Craddock, 88, a retired civil engineer with the Department of the Interior who specialized in rate structures for rural electric power systems, died Sunday at Suburban Hospital in Bethesda. He had been suffering from heart and kidney ailments.

Mr. Craddock was chief of the marketing and sales branch of the division of power in the Branch of Reclamation, a part of Interior, at the time of his retirement in 1960. He came to Washington in 1935, worked briefly with the Federal Communications Commission and joined the Rural Electrification Administration the following a year. He moved to Interior in 1942, when REA's functions were transferred there. His entire career at Interior was in the power division.

He received the department's meritorious service award on his retirement.

Mr. Craddock was born in the Oklahoma Indian Territory. He attended the University of Oklahoma and Rennsselaer Polytechnic Institute in Troy, N.Y., from which he graduated in 1917 with a degree in civil engineering. He worked for the Washington Department of Public Works in Olympia, Wash., before moving to this area.

He was a member of Sigma Xi, a scientific society, and of the American Society of Civil Engineers. He also was a member of the Sixth Presbyterian Church in Washington.

Survivors include his wife, the former Ruby E. Case, whom he married in 1914, of the home in Bethesda; a daughter, Virginia Oberlin, also of the home; a sister, Mrs. J. A. Maillian, of Olympia, Wash., and two grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Sixth Presbyterian Church, 16th and Kennedy Streets NW., Washington, D.C.