U.S. manufacturing activity grew more slowly in March, limited by weaker growth in production and new orders, but factories hired at a faster pace, according to a private-sector survey released Monday. The Institute for Supply Management (ISM) said its index of factory activity fell to 51.3 last month, down from 54.2 in February, which was the fastest growth since June 2011. A reading above 50 signifies expansion in the manufacturing sector, while a reading below 50 indicates contraction. The ISM index has shown manufacturing expansion for four consecutive months, but the drop in March growth was bigger than economists expected, suggesting some companies may have been wary of sharp government spending cuts that started March 1.