Thomas H. Countee Sr., 75, a retired Washington teacher, real estate agent and attorney who was active in civic, church and professional groups, died Dec. 13 at George Washington University Hospital. He had Alzheimer's disease.

Mr. Countee taught physics and mathematics in the D.C. public school system from 1948 until his retirement in 1972 from Coolidge High, where he had been chairman of the science department. In 1964, he received an award from the D.C. Board of Education for his work as a coauthor of the basic science and physics curriculum for the city's high schools.

He received his law degree at Howard University in 1949 and thereafter practiced law in partnership with George W. Parks. He obtained his first real estate license when he moved to Washington in 1943 to work for the government and for many years operated the Presto Realty Co.

In 1951 and 1952, he took a Fulbright Teaching Fellowship to the Hague, Holland. He received a number of fellowships from the National Science Foundation to study at American, George Washington and Howard universities. In 1957, he served on a panel to inspect military installations for the Defense Department.

Mr. Countee was born in Black Rock, Ark. He graduated from Lane College in Jackson, Tenn., and earned a master's degree in science at the University of Michigan. He taught in Alabama, North Carolina and Texas until 1942, when he went to work for the Army Signal Corps at Fort Monmouth, N.J. He moved to Washington the following year to do defense work at the National Bureau of Standards.

He was a resident of Washington until moving to the Manor Care nursing home in Wheaton two years ago.

Mr. Countee was a member of the D.C. and National bar associations, the National Education Association, the American Institute of Physics, the American Association of Physics Teachers, the Masons, the Elks, the Y.M.C.A. and the Urban League. He was a former president of the Laymen's League at All Soul's Unitarian Church.

Survivors include his wife, the former Arrieanna C. Tucker, to whom he was married for 46 years, of Washington; three sons, Thomas H. Jr., of Silver Spring, Charles E., of Washington, and Michael E., of Gaborones, Botswana, and two grandchildren.