Thomas Meloy, 85, a founder and former board chairman of the Melpar Corp., a leading electronics research company with headquarters in Falls Church, died of cardiac arrest Thursday at Sibley Memorial Hospital.

Mr. Meloy bought what was to become Melpar in 1944. The name of the company was made up of the first syllable of Mr. Meloy's name and that of Joseph Parks, a business associate who died in 1946. In 1951, the firm was bought by the Westinghouse Air Brake Co. for a reported $1 million. Mr. Meloy remained as its president until 1960 and as board chairman until 1965.

At one time, Melpar was the largest industrial employer in the Washington area with about 6,000 workers.

At the time of his death, Mr. Meloy was president of Meloy Laboratories Inc. in Springfield. The company recently was purchased by the Revlon Corp. Mr. Meloy also was chairman and chief executive officer of Isomet Corp.. an electronic and optics research and development company.

Mr. Meloy was born in Harrisburg, Pa. He graduated from Harvard College and then took an ebgineering degree at the Massachusetts Institute of Technology. He also studied at the Sorbonne in Paris.

During World War I, he was a major in the Army Corps of Engineers. He then spent three years working as an official on a railway in China. When he returned to the United States, he was an assistant to Henry L. Stimson, later secretary of war. He also worked for Bell Telephone Laboratories. With Joseph Parks, he later set up an engineering consulting firm in New York. He operated it until he bought what became Melpar.

Mr. Meloy was a member of the board of directors of the Arena Stage in Washington. He also was a member of the advisory board of the Center for Strategic and International Studies at Georgetown University.

Survivors include his wife, Claire, of the home in Washington; a daughter, Mrs. John Nussbaum, of Darien, Conn.; a son, Dr. Philip Meloy, of Morgantown, W. Va., and three grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Boy's Home, Covington, Va. 24426.