Felix J. Belair Jr., 70, a reporter and editor with the Washington bureau of The New York Times for more than 35 years, died Wednesday at the Winchester, Va., Memorial Hospital.

He had suffered a heart attack a week ago and had been in the hospital's intensive-care unit since then.

Mr. Belair, a native of Washington, joined The New York Times in 1929 after graduating from Georgetown University. He served with The Times' Washington bureau longer than any other reporter.

He was The Times' chief White House correspondent from 1936 to 1940, and was elected president of the White House Correspondents' Association in 1940.

That year he joined Time magazine as Washington bureau chief, a post he held until rejoining The New York Times in 1945.

After the war he specialized in economic reporting and spent a short time in Europe reporting on its post-war recovery.

During his years at The Times, Mr. Belair covered every presidential campaign from 1936 through 1964.

He served as news editor of the Washington bureau from 1953 to 1955, then spent three years in Stockholm as a Times' foreign correspondent, after which he returned to Washington. He was covering government regulatory agencies, including the Securities and Exchange Commission, when he retired in 1976.

He is survived by his wife, Margaret M., of the home in Alexandria; a son, Richard O., of Severna Park, Md; a daughter, Felicia B. Rigdon, of Columbia, Md.; two brothers, Dr. Joseph, of Galesville, Md., and Frank, of Stevensville, Md., and three grandchildren.

The family suggests that expression of sympathy be in the form of contributions to the Wardensville, W. Va., Rescue Squad.