By MARTIN CRUTSINGERWASHINGTON (AP) â¿¿ U.S. wholesalers boosted their stockpiles in January by the largest amount in 13 months even though their sales dropped sharply. Inventories at the wholesale level rose 1.2 percent in January compared with December when inventories had edged up a slight 0.1 percent, the Commerce Department said Friday. It was the biggest gain since a similar increase in December 2011. Sales at the wholesale level dropped 0.8 percent after being flat in December. Sluggish growth in stockpiles was a key reason the economy barely grew in the October-December quarter. But economists believe stronger job growth and other signs of an economic rebound will spur businesses to restock this quarter. Increased stockpiling supports economic growth by triggering greater factory production. The economy, as measured by the gross domestic product, grew at a barely discernible 0.1 percent rate in the fourth quarter. But many economists believe faster inventory building in the current quarter will help lift growth to a faster pace of around 2 percent in the January-March period. In January, the rise in stockpiles was led by a 3.4 percent gain in lumber inventories, a sign that building supply stores are boosting stockpiles in response to the rebound in home construction that has been occurring. Stockpiles of furniture, another industry that thrives when the housing market is gaining, rose 0.9 percent in January. Farm inventories, however, fell 1.5 percent after an even larger 5.5 percent drop in December. These declines likely reflected the impact of a severe drought last year which cut production. The various changes left wholesale inventories at $504.4 billion on a seasonally adjusted basis, 6.5 percent above the level of a year ago. In another sign of a rebounding economy, the Labor Department reported Friday that a burst of hiring in February added 236,000 jobs and reduced the unemployment rate to 7.7 percent, the lowest level in four years.