Frederick Ungar, 90, who fled the Nazi occupation of his native Vienna and established a publishing house in New York City that specialized in reference books and works on literature and films. His Frederick Ungar Publishing Co. helped popularize the works of Thomas Mann and Erich Fromm in this country. The firm's "Encyclopedia of World Literature in the 20th Century" is considered an essential work on writers from other countries. The company also published nearly 200 translations, among them Mann's last major work, "Reflections of a Nonpolitical Man." In Scarborough, N.Y., on Wednesday.