ORANGE, Calif./PHILADELPHIA (Reuters) – The Federal Reserve could well raise interest rates as soon as June, two top U.S. central bankers said on Friday, so long as economic data strengthens as expected from a dismal first quarter. The Fed has kept interest rates near zero since December 2008. The key, both Loretta Mester, president of the Cleveland Fed, and John Williams, president of the San Francisco Fed, said, is that by a quirk of the calendar there will be two more months of data for many of the key gauges the Fed follows, including the U.S.