WASHINGTON (Reuters) - U.S. business inventories were unexpectedly unchanged in January as increases in stocks at retailers were offset by declines at manufacturers and wholesalers.

The unchanged reading in business inventories reported by the Commerce Department's Census Bureau on Thursday followed a 0.3% increase in December.

Economists polled by Reuters had expected inventories, a key component of gross domestic product, to rise 0.2%.

Inventories increased 0.4% year-on-year 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 October-December quarter. Growth estimates for the first quarter are converging around a 2.0% pace.

Retail inventories increased 0.4% in January, instead of the 0.5% estimated in an advance report published last month. They advanced 0.6% in December.

Motor vehicle inventories climbed 0.8% as previously estimated. They accelerated 1.1% in December.

Retail inventories excluding autos, which go into the calculation of GDP, increased 0.3% as reported last month. They gained 0.4% in December. Wholesale inventories dropped 0.3% in January, while stocks at manufacturers dipped 0.1%.

Business sales declined 1.3% in January after being unchanged in December. At January' sales pace, it would take 1.39 months for businesses to clear shelves, up from 1.38 months in December.