Davis Eugene "Gene" Boster, 84, a career Foreign Service officer and two-time ambassador who served as head of the U.S. delegation to the 35-nation Conference on Security and Cooperation in Europe, died of cardiac arrest July 7 at his home in Arlington.

Mr. Boster headed the U.S. delegation to the conference in 1973 and 1974. The conference, which led to the Helsinki accord on human rights, was designed to recognize disputed post-World War II borders and establish a way to settle other disputes. Human rights became a key part of the treaty and gave the United States and other Western nations leverage to promote dissident groups in the Soviet bloc and urge greater freedoms for its residents.

From that assignment, Mr. Boster became the first U.S. ambassador to the new nation of Bangladesh in 1974, serving two years. He then went to Guatemala as ambassador.

He retired from the Foreign Service in 1979 to become director of Radio Liberty, a Munich-based American station broadcasting to the Soviet Union.

From 1980 to 1994, he was a Washington area independent consultant on foreign affairs, principally for the State Department and the intelligence community.

Mr. Boster was born in Rio Grande, Ohio, and graduated from Mount Union College in Alliance, Ohio. During World War II, he served in the Navy in the Atlantic and the Pacific, including an assignment as executive officer of the cargo ship Hennepin. He retired from the Naval Reserve in 1980 as a commander.

Trained in Russian during the final months of his wartime service, Mr. Boster joined the Foreign Service in 1947 and was sent to the U.S. Embassy in Moscow, later serving as desk officer for the Soviet Union and liaison officer to the Soviet and Eastern European delegations at the Japanese Peace Conference in San Francisco in 1951.

He later was a staff assistant to Secretary of State John Foster Dulles and officer in charge of Soviet Union affairs in Moscow from 1959 to 1962.

Other assignments included special assistant to the assistant secretary of state for inter-American affairs and undersecretary of state for economic affairs.

A lifelong tennis enthusiast, he was regularly on the Arlington YMCA courts until the week of his death.

His marriages to Mary Shilts Boster and Constanza Gamero Boster ended in divorce.

Survivors include five children from his first marriage, Davis E. Boster Jr. of Los Altos, Calif., Janis E. Boster of Red Bank, N.J., James S. Boster of Ashford, Conn., Thomas D. Boster of Napa, Calif., and Barbara A. Boster of Richmond, Calif.; a daughter from his second marriage, Valerie Boster of New York; eight grandchildren; and one great-granddaughter.