He died in Watch Hill, R.I., of complications of Parkinson's disease, his son, Leland Avery Westerfield, said.
Westerfield's former students in four decades of teaching also included Sens. John Kerry, D-Mass., and Joseph Lieberman, I-Conn., and assorted Cabinet officers, White House advisers and intelligence officials, who often cited his influence in framing their approach to public policy.
Cheney has repeatedly said Westerfield helped shape his hard-line approach to foreign policy. Westerfield, however, had characterized the current Bush administration as overly confrontational, calling that "precisely the wrong approach," The New York Times reported.
Westerfield earned his doctorate from Harvard, where he studied intelligence services. His thesis became his first book, "Foreign Policy and Party Politics: Pearl Harbor to Korea."
He taught at Harvard and the University of Chicago and spent a year studying Congress as a fellow of the American Political Science Association. In 1957, he joined Yale as an assistant professor of international relations, and stayed there until his retirement in 2001.