By John S. McClenahen Chairman Alan Greenspan and the 11 other voting members of the Federal Open Market Committee (FOMC) are widely expected to approve another 25-basis-point increase in the influential federal funds target rate when they next meet on Dec. 14. The increase would be the fifth this year and bring the target rate to 2.25%. But that should be it for awhile, believe the economists at Merrill Lynch & Co., New York. " . . . The funds rate, at 2.25%, would be 25 basis points above our median estimate for policy rates across the OECD [the 30-nation Organization for Economic Cooperation and Development], and our proprietary indicators suggest that the Fed does not need to raise rates any further," say Merrill's economists.