The Federal Reserve headquarters in Washington, DC.

The Federal Reserve ought not replace on a one-for-one basis its expiring "Operation Twist" program of $45 billion in purchases of longer-dated Treasurys a month because that may risk inflation, a senior U.S. central banker said on Monday.

St. Louis Federal Reserve Bank President James Bullard said fresh outright bond purchases to replace Twist, in which the Fed sells shorter-dated securities for longer date bonds, would have more impact on inflation and inflation expectations. Operation Twist expires at the end of the year.