WASHINGTON (Reuters) - U.S. wholesale inventories fell more than initially thought in September amid a sharp decline in motor vehicle stocks.

The Commerce Department's Census Bureau said on Thursday that wholesale inventories dropped 0.2% instead of the previously reported 0.1% dip.

Stocks at wholesalers rose 0.2% in August. Economists polled by Reuters had expected that the drop in inventories, a key part of gross domestic product, would be unrevised at 0.1%.

Inventories advanced 0.3% on a year-on-year basis in September. Wholesale motor vehicle inventories declined 1.7% after rising 0.3% in August.

Private inventory investment was a small drag on GDP in the third quarter. The economy grew at a 2.8% annualized rate in the July-September quarter.

Sales at wholesalers increased 0.3% in September after gaining 0.2% in August.

At September's sales pace it would take wholesalers 1.34 months to clear shelves, down from 1.35 months in August.