S. Paul Johnston, 86, a former director of the National Air and Space Museum and a man whose career in and around civil and military aviation included the editorship of Aviation Week magazine and service on the Strategic Bombing Survey at the end of World War II, died Aug. 9 at the Meridian-The Pines Nursing Center in Easton, Md. He had a heart ailment.

Mr. Johnston was a cadet pilot in the Army in World War I, an employe of the Aluminum Company of America working on alloys for use in aircraft in the 1920s, and the editor of the authoritative Aviation Week, a McGraw Hill publication, from 1933 to 1939. He then moved to Washington and for the next two years he was coordinator for research at the national Advisory Committee for Aeronautics, a predecessor of the National Aeronautics and Space Administration.

After this country entered World War II, he went into the Navy and became staff engineering officer for the Naval Air Transport Service in Hawaii. He held the rank of captain. Later he was an official of the Strategic Bombing Survey in Europe and Japan, which assessed the effectiveness of allied bombing offensives on the enemy's ability to make war.

In 1946, Mr. Johnston was named director of the Institute of Aeronautical Sciences in New York. In 1963, this merged with the American Rocket Society to form the American Institute of Aeronautics and Astronautics. Mr. Johnston was executive secretary of that organization when he took over as director of the National Air and Space Museum of the Smithsonian Institution.

He held that post from 1964 to 1969 when the museum occupied temporary quarters. Much of his work concerned planning its present modern quarters on the Mall.

"We have to lay the thing out so the man who has only an hour can follow a logical pattern and get the overall picture chronologically," he said in an interview with The Washington Post in 1965. "At the same time, it's got to be more than a stream of history from here to here. It's got to be a place where the person who has a specialized interest can see the 'whirlpools' along the stream of history."

In 1948, while at the Institute of Aeronautical Sciences, Mr. Johnston was executive director of the President's Air Policy Commission. In 1952, he did the same job for the President's Airport Commission.

After leaving the Air and Space Museum, he moved to the Eastern Shore of Maryland and served for a year as director of the Chesapeake Bay Maritime Museum at St. Michaels. He served on its board of governors until his death. He lived in Easton.

Mr. Johnston's military decorations included the Legion of Merit. He received an honorary doctorate from Adelphi College.

Mr. Johnston was a fellow of the American Institute of Aeronautics and Astronautics and an honorary fellow of the Royal Aeronautical Society and the Canadian Air and Space Institute. He was a member of the Federation Aeronautique Internationale, the Cosmos Club and the Talbot County Country Club.

His marriage to the former Carol Rhoades ended in divorce. His second wife, Catherine Johnston, died in 1948. His marriage to Claudine Johnston ended in divorce.

Survivors include his wife, the former Virginia Thomas of Easton; two children by his first marriage, James I. Johnston of San Francisco, and Mary Carol Ballard of Newport Beach, Calif.; a stepdaughter by his third marriage, Pierrette Johnston Collon of Lyon, France; 11 grandchildren, and three great-granchildren.