CORRECTED-(OFFICIAL)-US mortgage rates post steep 1-day drop

(Data vendor BestInfo corrects size of drop from 1-1/8 percentage point to 5/8 percentage point, retracts note of record one-day drop)

NEW YORK, Nov 25 (Reuters) - Rates on U.S. 30-year mortgages posted a 5/8 percentage point drop on Tuesday to 5-3/8 percent after the Federal Reserve said it would implement a $600 billion plan to support the mortgage securities market.

The Mortgage Point Monitor data series began in 1998, according to David Beadle, president of BestInfo, Inc., in Dover, Vermont.

(Reporting by Al Yoon)