Thomas Barrett Scott, 65, a Washington lawyer for more than 30 years, died of cancer Tuesday at Georgetown University Hospital.

Mr. Scott began practicing law here about 1945 and was associated with the firm of Casey, Scott and Canfield until last year. He also had practiced law in Montgomery County since 1966.

He was a resident of Kensington and was a Democratic Party election judge and precinct chairman in Montgomery County in recent years.

During World War II, Mr. Scott served in the Philippines as a legal assistant and instructor for the Navy Construction Battalions (Seabees).

He earned bachelor's and law degrees from New York University.

Mr. Scott was a member of the D.C. Maryland and American bar associations. He was active in All Souls Unitarian Church here and Cedar Lane Unitarian Church in Bethesda.

Survivors include his wife, Winifred E., of the home in Kensington; two daughters, Arlene B O'Connell, of Gaithersburg, and Deborah J., of Ann Arbor, Mich.; a sister, Frances E. Burke, of Englewood, Colo.; his stepmother, Doris Scott, of Castro Valley, Calif., and a granddaughter.

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