John D. Hickerson, 91, a career Foreign Service officer who served as U.S. ambassador to Finland and the Philippines, died of cancer and cardiac arrest Jan. 18 at Bethesda Retirement and Nursing Center. Mr. Hickerson retired from the Foreign Service in 1962 after having served three years as ambassador to the Philippines. He was ambassador to Finland from 1955 to 1959. He had served for two years before that as deputy commandant for foreign affairs at the National War College. From 1949 to 1953, Mr. Hickerson was assistant secretary of state for international organization affairs, and in that capacity dealt extensively with issues involving the Korean War and other matters in the Far East. A resident of Washington, he was born in Crawford, Tex., and graduated from the University of Texas. Early Foreign Service assignments included duty in Rio de Janeiro and Ottawa. During the 1930s, Mr. Hickerson served in the State Department's Office of European Affairs, then during World War II was a member of the joint board of defense for the United States and Canada. He was an adviser to the U.S. delegation at the Dumbarton Oaks conference and at the United Nations organizing conference in San Francisco in 1945, and he served later as chairman of the working group that drafted the treaty establishing NATO. Mr. Hickerson also had been a regular lecturer at the School of Foreign Service of Georgetown University. He was on the board of directors of the Atlantic Council and was a member of the Metropolitan Club and DACOR (Diplomatic and Consular Officers Retired). His wife, Vida Corbin Hickerson, died last June. Survivors include a son, John H. Hickerson of Chevy Chase; three grandchildren, and two great-grandchildren.