Lily Auchincloss, a philanthropist and major supporter of the Museum of Modern Art, the American Academy in Rome and the Cathedral of St. John the Divine, died on Friday at her home in Manhattan. She was 74. The cause was cancer, said her daughter, Alexandra Herzan. Mrs. Auchincloss was well known in New York cultural and social circles as an active and generous supporter of the arts with a keen interest in architecture and design. A trustee at the Museum of Modern Art since 1971, she served on more than one-third of the museum's many trustee committees, including those of painting and sculpture, drawings and prints and illustrated books, and had been chairwoman of the museum's architecture and design committee since 1981. Mrs. Auchincloss was born on April 5, 1922, in Newark. Her father, Arnold Louis van Ameringen, who was born in Holland, founded the International Flavors and Fragrances Company. Her mother, Hedwig Pfaltz van Ameringen, who died last month at the age of 95, was a major supporter of the New York Philharmonic. She graduated cum laude from Radcliffe in 1944. From 1944 to 1958, Mrs. Auchincloss worked in New York City as an editor on magazines and newspapers, including Look, The World-Telegram, The Herald Tribune, Glamour, Harper's Bazaar and McCall's. In 1956, she married Douglas Auchincloss, a writer at Newsweek. They were divorced in 1979. In 1977, Mrs. Auchincloss became the first woman to join the board of the Cooper Union. She also served on the board of Japan Society, and was a director of the Municipal Arts Society and a Fellow for Life of the Morgan Library. In addition to her daughter Alexandra Herzan, of Manhattan, she is survived by a brother, Henry P. van Ameringen of Manhattan; a sister, Patricia Kind of Huntingdon Valley, Pa., and a granddaughter.