Warburg was a founding father of the American Ballet, which was George Balanchine's first American company and the precursor of the New York City Ballet. He was also a founder of the Museum of Modern Art and served on its board of trustees from 1932 to 1958. From 1939 to 1965, with time out for military service in World War II, he was a co-chairman of the Joint Distribution Committee. He was also the national chairman of the United Jewish Appeal from 1950 to 1955 and served for a time as president of the United Jewish Appeal of Greater New York. In addition, he was a member of the New York State Board of Regents from 1958 to 1975. He was the youngest of five children of Felix and Frieda Warburg. His mother was the only daughter of Jacob Schiff, the merchant banker and financier. His father was a partner in Kuhn, Loeb & Company, the investment banking firm, and a philanthropist. He graduated from Middlesex School in Concord, Mass., and in 1930 from Harvard. Warburg was also active as an art collector, and he aquired works by such modern artists as Picasso, Matisse, Hopper, O'Keeffe, Lachaise, Klee, Miro, Brancusi and Calder, some of which he later donated to the Museum of Modern Art and other museums. In addition to his son, of Wilton, Mr. Warburg is survived by his wife, the former Mary Whelan Prue Currier; a daughter, Daphne Astor of Cambridgeshire, England; eight grandchildren, and four great-grandchildren.