WASHINGTON, April 21 (Reuters) - U.S. business inventories increased slightly more than expected in February amid a sharp rebound in stocks at wholesalers, suggesting that inventory investment could add to economic growth in the first quarter.

Inventories advanced 0.4% after being unchanged in January, the Commerce Department's Census Bureau said on Tuesday. Economists polled by Reuters had expected inventories, a key component of GDP and one of the most volatile, increasing 0.3% in February.

Inventories increased 1.3% year-on-year in February. The Census Bureau has now caught up on the release of this indicator after delays caused by last year's government shutdown. March business inventories will be released on schedule next month.

Retail inventories increased 0.2% in February after rising 0.3% in January. Wholesale inventories rebounded 0.8% while stocks at manufacturers gained 0.1%.

Business inventories made a small contribution to the 0.5% annualized GDP growth pace in the fourth quarter. The Atlanta Federal Reserve is currently forecasting GDP increased at a 1.3% rate in the first quarter. The economy grew at a 4.4% pace in the July-September quarter.

Business sales shot up 1.7% in February after rising 0.6% in January. Sales at retailers increased 0.7%. At February's sales pace, it would take 1.33 months for businesses to clear shelves, down from 1.35 months in January.