Leo Clifford Young, 90, a retired scientist with the Naval Research Laboratory whose work helped lead to the development of radar, died Jan. 16 at the Regency Nursing and Rehabilitation Treatment Center in Forestville, where he had resided for about three years. He had arteriosclerosis.

Mr. Young had worked at the laboratory from 1923, when it opened officially, until his retirement in 1967. He had joined the Navy during World War I and later worked for it as a civilian employe after the war.

He was credited in 1922 with the development of radio equipment used to make the first observations and detection of ships moving on the Potomac River. The method is now known as continuous-wave radar.

In 1930, Mr. Young was in charge of research that resulted in the first detection of aircraft by radio. Four years later, he was responsible for research that led to the development of the first system utilizing radio pulses for range determination of stationary or moving objects. Similar work was under way at the Army Signal Corps and in Britain and Germany. This system became known as radar, an acryonym for radio detection and ranging.

Mr. Young was a pioneer in amateur radio and helped conduct the original research that led to the utilization of high frequencies for worldwide radio communications.

His many honors included the Presidential Certificate of Merit from President Truman in 1946, the Stuart Ballantine Medal of the Franklin Institute in 1957 and the Navy Department's Distinguished Civilian Service Award in 1958.He also was awarded a 50-year gold certificate by the Quarter-Century Wireless Association in 1966.

Mr. Young was a fellow of the American Association for the Advancement of Science and the Institute of Electrical and Electronic Engineers and a member of the Research Society of America and the Society of Photographic Engineers.

Survivors include his wife, Mabel, and two sons, Leo C. Jr. and Richard A., all of Oxon Hill, two grandchildren and a great-grandchild.