WASHINGTON (Reuters) - U.S. wholesale inventories fell more than initially thought in January, which could negatively impact economic growth estimates for the first quarter.

The Commerce Department's Census Bureau said on Wednesday that wholesale inventories dropped 0.3% instead of dipping 0.1% as estimated last month. Stocks at wholesalers increased 0.4% in December. Economists polled by Reuters had expected that inventories would be unrevised.

Inventories are a key part of gross domestic product. They fell 2.5% on a year-on-year basis in January. Private inventory investment subtracted 0.3% percentage point from GDP growth last quarter after providing a large boost in the third quarter. The economy grew at a 3.2% annualized rate in the fourth quarter.

Growth estimates for first quarter are converging around a 2.0% pace.

Wholesale motor vehicle inventories rose 0.7%. But there were decreases in stocks of farm products, chemicals, apparel and paper. Excluding autos, wholesale inventories dropped 0.4% in January. This component goes into the calculation of GDP.

Sales at wholesalers declined 1.7% after rising 0.3% in December. At January's sales pace it would take wholesalers 1.36 months to clear shelves, up from 1.34 months in December.

(Reporting by Lucia Mutikani)