General Motors Co said on Thursday that its U.S. September auto sales fell 45 percent, pressured by weak consumer confidence, low inventory levels and the end of the U.S. government cash for clunkers incentives.

GM said that sales fell to 156,673 vehicles in September, from 284,300 a year earlier when company incentives supported sales. The automaker expects to post a 21 percent market share, its highest of the year so far.

The results stood in contrast to Ford Motor Co , the only large U.S. automaker to avoid a restructuring in bankruptcy supported by the U.S. government this year, which posted a 5 percent U.S. sales decline in September. Ford shares were down 20 cents or 2.8 percent at $7.01 on the New York Stock Exchange on Thursday afternoon

Rival Chrysler's U.S. sales fell 42 percent in September.

GM said retail sales fell 46 percent in September from a year earlier and fleet sales fell 43 percent.

GM left its prior fourth-quarter North American production forecast of 655,000 vehicles intact. That plan represents a 20 percent cut from the fourth quarter of 2008.

The automaker, which emerged from bankruptcy in July, said it ended September with about 424,000 vehicles in stock, down about 41 percent from a year earlier. The inventory included 157,000 cars and 267,000 trucks.

(Reporting by David Bailey and Kevin Krolicki, editing by Matthew Lewis)