-- During her first four months on the Federal Reserve Board, Janet L. Yellen has been the invisible central banker, avoiding public appearances and press interviews. But Yellen at last is emerging to position herself as an inflation hawk. She may have learned from the debut of another new Clinton appointee to the Fed, Vice-Chairman Alan S. Blinder, who got into trouble with remarks that made him look soft on inflation to Wall Street. Yellen, also suspected of being an inflation dove, isn't taking any chances with the Street. In an interview with BUSINESS WEEK, the former University of California-Berkeley economist says: "I don't want the inflation rate higher when I leave here than it is now."