Secretary of State George Shultz has been appointed an honorary fellow of the Hoover Institution at Stanford University. Institution Director W. Glenn Campbell said the university's board of trustees approved Shultz's nomination at its December meeting. Shultz becomes the fourth honorary fellow of the campus-based conservative "think tank," joining President Reagan and Nobel laureates Alexander Solzhenitsyn and Friedrich A. von Hayek. Campbell called Shultz "one of America's most distinguished statesmen, whose association . . . will be an invaluable asset both to the institution and to Stanford University." Shultz is expected to take up residence at the institution at the end of his term in the Reagan Administration and, Campbell said, would most likely resume his post as the Jack Steel Parker professor of international economics at the Stanford Graduate School of Business.