WASHINGTON -- The US manufacturing sector resumed expansion in September after three consecutive months of contraction, a good sign for the struggling economy,a leading industry survey showed on Monday.

The US Institute of Supply Management (ISM) said the manufacturing index, also known as the purchasing managers index ( PMI), rose to 51.5 percent in September, up from the estimate of 49.6 percent in August.

It was the first growth in four months. A reading above 50 percent indicates that the manufacturing sector is generally expanding, while a reading below 50 percent indicates contraction.

New orders, production and employment indexes all rose for the month, but the measurement of production remained below the 50 percent growth threshold.

Manufacturing has been a bright spot in output and employment since the recession ended in June 2009. But the sector has shown signs of weakening in recent months.

The US economy grew at an annual rate of 1.3 percent in the April-June quarter, down from a 2 percent rate in the first three months.