Thomas Halvor Olsen, 63, a retired senior accountant of the Central Intelligence Agency who specialized in commercial support to agency operations, died of cancer Wednesday at Circle Terrace Hospital in Alexandria.

Mr. Olsen joined the CIA in 1954. At retirement in 174, he was awarded a certificate of distinction for his work at the CIA.

Born in Staten Island, N.Y., Mr. Olsen attended New York University and St. John's University. After serving as a major in the Army during World War II, he spent 25 years in the reserves, attaining the rank of lieutenant colonel before retiring.

After the war, he lived in Kansas City, Mo., and New Albany, Ind., working in various jobs, among them the Office of Price Administration. He moved to Alexandria in 1954.

Mr. Olsen was a member of the Masonic East Gate Lodge of Kansas City, Mo., and past president of the Masonic organization, the National Sojourner. He is a past treasurer of the Alexandria Boys Club and a member of the Fairlington United Methodist Church.

Survivors include his wife, Bettie, of the home in Alexandria; three sons, Thomas Jr., of Arlington; Christopher J., of Front Royal, Va., and Lawrence D., of Alexandria, and his mother, Eleanor L. Olsen, of Fairview, N.J.

The family suggests that expressions of sympathy may be in the form of contributions to the American Cancer Society.