Dec 12 (Reuters) - Wall Street's main indexes opened

flat to lower on Thursday after the S&P 500 and the Nasdaq ended

the previous session on a positive note, while investors parsed

through hot economic data ahead of the Federal Reserve's

meeting.

The Dow Jones Industrial Average rose 20.1 points, or

0.05%, at the open to 44,168.66. The S&P 500 fell 9.9

points, or 0.16%, at the open to 6,074.29​, while the Nasdaq

Composite dropped 87.6 points, or 0.44%, to 19,947.336

at the opening bell.