J Roderick MacArthur

An international marketer for limited-edition collectors' plates, such as commemorative Christmas plates. A computerized system operating on the trading floor enables buyers to place orders and receive immediate confirmation. The concern operates exchanges in Canada, four European cities and in Australia. The younger Mr. MacArthur also established his own private philanthropy, the J. Roderick MacArthur Foundation, which supports various human rights and civil liberties causes. Mr. MacArthur influenced the larger foundation to join the Atlantic Richfield Foundation in purchasing Harper's Magazine when the 130-year-old publication was on the verge of folding in 1980. His son, John R. MacArthur, known as Rick, became Harper's publisher in Nov. 1983, serving without salary. John Roderick MacArthur - he preferred to be called ''Rod'' - was born in San Francisco on Dec. 21, 1920, attended Rollins College in Winter Park, Fla., and also the University of Mexico. During World War II, he joined the civilian ambulance corps of the American Field Service and served with the French Army and in a French resistance unit. At the war's end, he remained in Paris as a correspondent for the United Press, and worked also as a free-lance writer. Many years later, he would say his interest in newspapers and in rescuing Harper's was influenced by his father's brother, the late dramatist Charles MacArthur, who was co-author of the play ''The Front Page.'' He returned to the United States in 1952 and worked as a freelance writer until he came to Chicago to supervise new business for his father's Citizens Bank and Trust Company. In 1980, Mr. MacArthur purchased Hammacher Schlemmer and revamped the retail store's inventory. Besides his son Rick, Mr. MacArthur is survived by his wife, the former Christiane L'Entendart, whom he married in Paris in 1947; a son, Gregorie, a journalist; and a daughter, Solange, a medical student.