THE PALACE FILE By Nguyen Tien Hung and Jerrold L. Schecter. Illustrated. 542 pp. New York: Harper & Row.
WRITTEN largely from a Saigon perspective, this book provides significant new data on United States relations with South Vietnam from 1968 to 1975 and fresh insights into the character of Nguyen Van Thieu, the general whom the United States supported as South Vietnam's President from 1967 to 1975. An extraordinary collection of previously undisclosed exchanges of letters between Mr. Thieu and Presidents Nixon and Ford combine with the authors' interviews with many key Americans and Vietnamese to make this an important study.
Nguyen Tien Hung, an American-trained economist who currently teaches at Howard University, was with the International Monetary Fund before being appointed special assistant to President Thieu in 1973. He later became Minister of Economic Development and Planning and one of Mr. Thieu's closest advisers. Jerrold Schecter, author of an earlier book on Vietnam, ''The New Face of Buddha,'' covered Vietnam for Time magazine in the early 1960's; from 1971 to 1975 he was the magazine's White House correspondent and then its diplomatic editor.