World Bulletin / News Desk
The Dow fell 3 points to begin the day at 21,324 points and the S&P 500 lost 1 point to 2,438 points.
The Nasdaq slipped less than 1 point to start trading at 6,219 points.
The Fed will announce its interest rate decision at 1800 GMT, and Chair Janet Yellen will hold a news conference at 1830 GMT.
The market is highly anticipating a rate hike from the central bank, which last raised its benchmark interest rate in March, experts said.