Washington--Jan. 31--The Federal Reserve Bank cut interest rates by half a percentage point for the second time in a month as Chairman Alan Greenspan worked to keep the economic slowdown from growing into a recession. The move reduced the federal funds rate target to 5.50%, partly unwinding the six rate increases that boosted borrowing costs by 1.75 percentage points from June 1999 through May 2000. The bank also reduced the discount rate to 5.00% from 5.50%.