WASHINGTON (MarketWatch) - U.S. retail sales rose in May at the fastest rate in three months, led by higher demand for autos, building materials and groceries. Retail sales rose a seasonally adjusted 0.6% last month, or by 0.3% excluding the auto sector, the Commerce Department said Thursday. Economists polled by MarketWatch had forecast retail sales to climb by 0.5% overall and be unchanged minus autos. Excluding gasoline stations, retail sales were up 0.6%. The details of the retail report were somewhat mixed, however. Sales rose for auto dealers, suppliers of building materials, grocery stores, and Internet retailers. Sales fell for electronics, appliances, clothes, home furnishings and bars and restaurants. Retail sales account for about one-third of consumer spending, the main propeller of economic growth. In the past year, retail sales have risen a solid but unspectacular 4.3%. In April, sales were unrevised at a 0.1% increase. The 0.3% decline in sales in March was also unchanged.