Thomas D. Iorio, 79, the deputy sereant-at-arms of the House of Representatives and an employe there since 1945, died of lung cancer Saturday at his home in Silver Spring.

Mr. Iorio, who was born in Brooklyn, began his public career as a deputy sheriff in Kings County, which is Brooklyn. For the rest of his life, he kept in touch with the Democratic Party organization in Brooklyn. In 1945, he came to Washington under the auspices of former Rep. John Rooney, a Brooklyn Democrat. He went to work for the sergeant-at-arms, serving as an aide on the House floor.

In nonelection years, Mr. Iorio organized trips to New York sponsored by the New York congressional delegation. He continued this activity from the mid-1940s until recently.

In 1976, he received the John W. McCormack Award, which is named after the late Speaker of the House and it presented to House employes who have provided outstanding service to representives. In the same year, he was named "Man of the Year" by the Doorman's Association.

In 1974, Mr. Iorio received a decoration from the Italian government for his efforts to improve Italian-American relations.

Survivors include his wife, Clara, of Silver Springs; a daughter, Connie Furlong of Mount Airy, Md.; a son, Carmine, of Silver Spring; three sisters, Mary Muratore and Molly Barbera, both of Ozone Park, N.Y., and Anne Cusare of Margate, Fla., and six grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Villa Rosa Italian Home for the Aged, Mitchellville, Md.