Dr. Ralph DeBelles, 57, a retired assistant to the dean of the George Washington University graduate school, who was a retired Air Force lieutenant colonel, died of cancer March 8 at his home in Bradenton, Fla. He had lived in Alexandria since 1964 before moving to Bradenton earlier this year.

Dr. DeBelles was a native of New York and a graduate of Syracuse University in Syracuse, N.Y., and the State University of New York. He earned his doctoral degree from George Washington University.

He joined the old Army Air Forces during World War II and served in the Pacific. After the war, he worked as a teacher in New York. He returned to active duty during the Korean conflict and served in the Pacific. His last tour of duty was at the Pentagon. He retired from the Air Force in 1970.

Dr. DeBelles joined the faculty of George Washington University in 1970. Before joining the graduate school, he was assistant dean of the College of General Studies. He retired a second time in 1981.

He was a member of the Army-Navy Club and the Rehoboth Bay Sailing Association in Rehoboth Bay, Del., where he maintained a summer residence.

Survivors include his wife, Sally, of Bradenton; a daughter, Tracy, of Arlington; two sons, Greg, of Los Angeles, and Buff, of Bradenton; his mother, Angeline DeBelles of Oswego, N.Y., and two sisters, Agatha Kelly of Oswego and Charlotte Stewart of Fairfax, Va.