Marvin Schuldenfrei, 63, an aeronautical engineer and research scientist who helped conduct early federal experiments in space flight, died of a heart attack May 12 at Washington Hospital Center.

Mr. Schuldenfrei, who lived in Bethesda, was born in New York City.

He graduated from the Guggenheim School of Aeronautics at New York University in 1939. Then he worked with the National Advisory Committee for Aeronautics at Langley Aeronautical Laboratory in Hampton, Va., until 1946.

That year he went to the Navy Department as an expert in air-to-air missile design and development.

In 1959, he joined the newly formed National Aeronautics and Space Administration (NASA), where he was involved in long-range planning related to manned and unmanned space flight.

During his career, Mr. Schuldenfrei helped conduct theoretical and experimental research on advanced aircraft design and helped design the nation's most advanced wind tunnel of his day.

In the late 1960s, he worked briefly for IBM and Science Application Inc., then returned to federal service as chief engineer of the Joint Navy/Commerce Department surface effects ship program. He retired in 1976.

Survivors include his wife, the former Rosalyn Nasoff, of Bethesda; two sons, Neil, of Bethesda, and Dr. Jeffrey, of Catonsville, and a sister, Ruth Bortner of New York City.