Brands, H. W. Inside the Cold War: Loy Henderson and the Rise of the American Empire 1918-1961 (1991) pp 196-230; Loy Henderson was US Ambassador, 1948-51
Galbraith, John K. Ambassador's journal: a personal account of the Kennedy years (1969) online, he was US ambassador to India 1961-63
U.S. Department of State. Foreign Relations of the United States (FRUS), many volumes of primary sources; the complete texts of these large books are all online. See Guide to FRUS. For example, Foreign Relations of the United States, 1969–1976, Volume XI, South Asia Crisis, 1971 was published in 2005 and is online here. The most recent volumes are Foreign Relations of the United States, 1969–1976, Volume E–7, Documents on South Asia, 1969–1972 (2005) online here and Foreign Relations of the United States, 1969–1976, Volume E–8, Documents on South Asia, 1973–1976 (2007) online here.