Stewart ("Sandy") Richardson, a former editor-in-chief at Doubleday who published many distinguished authors there and then went on to head two publishing companies of his own, died July 7 in a New York hospital. He was 78. Four of the books Richardson published at Doubleday received Pulitzers, including Wallace Stegner's Angle of Repose and Bill Goetzmann's The Exploration of the American West. He published Rose Fitzgerald Kennedy's Times to Remember, as well as books by Robert and Edward Kennedy, and his other authors included John Updike, Bruce Catton, James Dickey, William Goldman, Willie Morris, Lonnie Coleman and Pierre Salinger. Later, he headed Richardson & Steirman, which first published Mikhail Gorbachev here, and Birch Lane, part of Carol Publishing. He is survived by his wife, St. Martin's Press president and publisher Sally Richardson, two children and four grandchildren.