John Gilbert Reid, 78, a historian in the State Department for more than 30 years and an expert on Far Eastern affairs, died of cancer Nov. 7 in Doctor's Hospital of Prince George's County.

Dr. Reid, the son of American missionaires in China, had lived in that country for more than 20 years. He was educated at Hamilton College in Clinton, N.Y., and at the University of California at Berkeley, where he earned master's and doctoral degrees in history. He taught at the University of Pennsylvania, the University of California, Washington State College, and the University of Oregon before joining the State Department in 1939.

A diplomatic historian, he helped select and annotate documents published by the State Department in annual volumes of "The Foreign Relations of the United States." His specialty was the Far East. In addition to contributing to "The Foreign Relations of the United States," he carried out special studies on China and Japan. He retired from the department in 1971, but continued his work as a consultant until 1973.

Dr. Reid served in the Army during World War I. He was a member of the American Historical Association.

Survivors include his wife, Lieselotte Arlt Reid, both of the home in College Park; two daughers, Lilo Valerie sheahan, of Silver Spring, and Elizabeth Jean George, of Wayson Corner, Md., and a grandson.