Harcourt Sontag, 80, a retired aeronautical engineer with the Navy Department's Bureau of Aeronautics, died of cancer Tuesday at his home in Arlington.

Mr. Sontag began his government career with the National Bureau of Standards in 1917. There he helped develop instrument panels for aircraft. He joined the Bureau of Aeronautics about 1941.

During World War Ii, he served in the Navy with the Seventh Fleet in the Southwest Pacific.

He later returned to the Bureau of Aeronautics, where he helped develop oxygen masks, air-conditioning systems, and improved instrumentation design. He retired in 1966.

Mr. Sontag was a native of Washington and had resided in Arlington for the last 47 years. He was a 1928 graduate of George Washington University, where he earned a degree in mechanical engineering.

He was a member of the Institute of Aeronautical Sciences and the Washington Society of Engineers. He also was a member of the Army-Navy Country Club and the Arlington Host Lions Club.

Mr. Sontag sang in the Washington Cathedral Boys Choir when he attended St. Alban's School. He was a member of St. John's Episcopal Church in Georgetown for 22 years and was a tenor soloist there. At the time of his death, he was a member of St. Peter's Episcopal Church in Arlington, where he had been a member of the vestry and a lay reader.

Survivors include his wife of 52 years, the former Annabelle Lloyd, of Arlington; two sons, Lloyd, of Stafford, Va., and Donald, of Media, Pa., and two grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Arlington Cancer Society.