Dr. John G. Trump, a retired teacher and engineer, died Thursday at his home in Cambridge, Mass., after a long illness. He was 78 years old.

Dr. Trump began studying the voltage-insulation properties of high vacuum and com- pressed gases while a faculty member at the Massachusetts Institute of Technology. Working with Prof. Robert J. Van de Graaff, he designed one of the first million-volt X-ray generators. Used initially for clinical purposes at the Collis P. Huntington Memorial Hospital in Boston in 1937, it was a development that provided additional years of life to cancer patients throughout the world.

In 1946, Dr. Trump, along with Dr. Van de Graaff and Dr. Denis M. Robinson, founded the High Voltage Engineering Corporation, which developed the Van de Graaff electrostatic generator.

In World War II Dr. Trump was influential in the development of radar and short-wave radar equipment. He was appointed director of the British branch of the M.I.T. Radiation Lab in 1944.

After the war. Dr. Trump, while still on the faculty at M.I.T., became associated with the Department of Radiology at the Lahey Clinic in Boston and later became chairman of its board. Under his direction rotational radiation therapy was developed, ”an idea that created quite a stir in those days,” he recalled later. He also conceived and developed the use of high-energy electrons in the treatment of superficial skin lesions.

He Received Emeritus Status

He became professor emeritus at M.I.T. in 1973, remaining on as a senior lecturer.

He was the author of nearly 80 scientific publications and the recipient of many awards, including His Majesty’s Medal, given by George VI in 1947; the President’s Certificate of Merit, presented by President Truman in 1948; and the Lamme Medal, awarded in 1960 by the American Institute of Electrical Engineers. In 1983, he was the recipent of the National Medal of Science.

He was a graduate of the Polytechnic Institute in 1929, received a master’s degree in physics from Columbia University in 1931 and a doctorate from M.I.T. in 1933.

Dr. Trump is survived by three children, John Gordon Trump of Watertown, Mass., Christine Philp of Pittsfield, Mass., and Karen Ingraham of Los Alamos, N. M.; and six grandchildren. He was the brother of Frederick C. Trump and the uncle of Donald Trump, New York real estate developers.

A funeral service will be held Sunday at 2:30 P.M. at the Unitarian Church in Winchester, Mass.

photo of Dr. John Trump