The chairman of the Senate Banking Committee expressed reservations yesterday about President Carter's appointment of G. William Miller to head the Federal Reserve Board, but said he wouldn't oppose the nomination and expected to see it approved.

Sen. William Proxmire (D-Wis.) said he was "concerned" because Miller is a businessman and has "no real experience" in dealing with monetary policy or banking. "I don't think we should have a man who will have to have on the job training," he said.

At the same time, however, Proxmire said he does not intend to try to block the nomination when the Banking Committee begins confirmation hearings in January, and "would be very surprised" if the Senate balks at approving Miller for the Fed post.

"I'm not necessarily opposed or supportive of the nomination," Proxmire said in a telephone interview yesterday. However, he added, even if Miller follows the policies of Arthur F. Burns, the present Fed chairman, exactly, he will be doing it "without Burns" experience."

"I'm not sure it wouldn't have been better to leave Burns where he was," the senator said.

Proxmire's remarks were among several expressions of doubt voiced by political and business figures yesterday in the wake of the initial round of praise for the nomination that followed the President's announcement of the switch on Wednesday.

Jack Carlson, vice president and chief economist of the U.S. Chamber of Commerce, also issued a guarded statement, noting that "the President has selected a person whose monetary policy positions are unkown." He said Burns' ouster would "create uncertainty about this nation's commitment to fight inflation."

However, most businessmen continued to be at least outwardly pleased by the nomination. Miller, 52, is chairman and chief executive officer of Textron, Inc., a Providence-based conglomerate. He has served as a director of the Federal Reserve Bank of oston, a part-time post.

If confirmed by the Senate, Miller wou'd take office as chairman on February 1, filling the term now held by board member David M. Lilly, 60, which expires January 31.

If Burns decides to step down as a governor before his own term runs out, in January of 1984, Carter will have had the opportunity to name three of the board's seven members by the end of his first term as President. The term of Fed governor Philip E. Coldwell, 63, runs out in January 1980.