Alvin A. Dewey, chief investigator of the 1959 killings chronicled in the book and movie ''In Cold Blood,'' died Friday at a hospital here after suffering a stroke at his home. He was 75 years old.

Mr. Dewey, who retired in 1975 after nearly 40 years in law enforcement, became internationally known for his investigation of the Nov. 15, 1959, murder of Herbert Clutter and three members of his family in their rural home in Holcomb. Two convicted killers, Perry Smith and Richard Hickock, were executed five years later.

Truman Capote wrote ''In Cold Blood,'' a graphically detailed account of the case that was turned into a movie in which John Forsythe portrayed Mr. Dewey, a three-term Finney County sheriff who later worked for the Kansas Bureau of Investigation for 20 years. Biggest, But Not Toughest Case

At his retirement, Mr. Dewey told reporters that while the Clutter case was possibly his biggest in terms of publicity, others among the 200 homicides he investigated were more difficult.

Jack Ford, assistant director of the K.B.I., said Mr. Dewey had a knack for getting along with everyone. ''He could talk to a suspect without degrading him.'' Mr. Ford said. ''He could be both firm and compassionate. He was one of the best law-enforcement officers I ever worked with. He had the knowledge, experience, and personality it took to be a highly qualified and effective officer.''

Mr. Dewey is survived by his wife, Marie, and two sons, Alvin A. Dewey 3d of Eugene, Ore., and Paul Dewey of Sisters, Ore.

Alvin A Dewey