WASHINGTON, April 1 (Reuters) - U.S. business inventories unexpectedly fell in January amid a large decline in stocks at wholesalers, suggesting inventory investment could weigh on economic growth in the first quarter.

Inventories dipped 0.1% after being unchanged in December, the Commerce Department's Census Bureau said on Wednesday. Economists polled by Reuters had expected that inventories, a key component of GDP and one of the most volatile, would edge up 0.1% in January.

Inventories increased 1.0% on a year-over-year basis in January. The Census Bureau is still catching up on data releases following last year's government shutdown. Retail inventories rose 0.3% in January after gaining 0.1% in December.

Wholesale inventories dropped 0.5% while stocks at manufacturers edged up 0.1%.

Business inventories added to the 0.7% annualized GDP growth pace in the fourth quarter, despite marking their third straight quarterly decline. The economy grew at a 4.4% pace in the July-September quarter.

Business sales increased 0.3% in January after rising 0.7% in December. Sales at retailers eased 0.1%. At January's sales pace, it would take 1.35 months for businesses to clear shelves, down from 1.36 months in December.