John O. Hardesty, 78, a retired chemist with the Department of Agriculture who specialized in the production and use of chemical fertilizers, died of a respiratory ailment Friday at Leland Memorial Hospital, Riverdale.

Mr Hardesty was born in Westfield, Ill. He served in the Army during World War I and later in the reserves. He graduated from DePauw University and earned a master's degree at Michigan State for six years before moving to the Washington area in 1930 and joining the Department of Agriculture. He retired in 1965.

He was a member emeritus of the American Chemical Society. He was a former chairman of the society's division of fertilizer and soil chemistry and coeditor of the section on soils and fertilizers of Chemical Abstracts, a society publication. He also had served on the editorial advisory board of the Journal of Agricultural and Food Chemistry.

Mr. Hardesty was active in church and community affairs. He held several positions in the Clarendon Presbyterian Church in Arlington, where he lived for several years, and the Riverdale Presbyterian Church in University Park. He had been a member of the Park Board of University Park and had been a supporter of the Boy Scouts.

Survivors include his wife, Irene Austin Hardesty. of the home in Hyattsville; a son, David Austin Hardesty, of Arlington, Texas; a daughter, Carolyn H. Murrow, of Gaithersburg, Md.; a sister, Vera Thompson, of Otsego, Mich., and five grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Riverdale Presbyterian Church, 6513 Queens Chapel Rd., University Park.