WASHINGTON (MarketWatch) — American manufacturers resumed growing in September after a three-month contraction, outperforming most of the rest of the world, according to a closely followed survey.

The Institute for Supply Management’s index of purchasing managers — the executives who order raw materials and other goods — climbed to 51.5 from a three-year-low of 49.6 in August. It was the highest score since May.

The modest improvement in U.S. manufacturing suggests companies are weathering a global economic slowdown better than their counterparts in other nations. Gauges for the biggest economies in Europe and Asia show that the manufacturers in those regions are still undergoing contraction.

U.S. shows more improvement in September that other large economies.

The ISM report easily surpassed Wall Street expectations: Economists surveyed by MarketWatch had forecast the index to remain under 50 for the fourth straight month, at 49.7.

In U.S. markets on Monday, stocks extended their rally, with the Dow Jones Industrial Average DJIA, -0.47% up 145 points in recent activity and other equity benchmarks showing lesser gains as traders digested the ISM data. See Market Snapshot

Readings above 50 indicate business is improving; readings under 50 signal deterioration.

The scene at a Ford assembly plant in Louisville earlier this year. Reuters

“While 51.5 is still pretty low, consistent with very weak growth in manufacturing output, the improvement from a month ago is significant,” said Jim O’Sullivan, chief economist at High Frequency Economics.

A jump in new orders — the index rose to 52.3 from 47.1 — underscored the gains in the September ISM report. The production index also gained, up 2.3 points to end at 49.5.

“There are a lot of signs that are good here,” said Bradley Holcomb, chairman of the ISM survey committee, in a call with reporters. “To me it looks promising.”

Eleven of the 18 U.S. manufacturing industries surveyed by ISM reported growth in September. Six of the remaining seven saw a contraction.

The response of executives was somewhat mixed. Executives in the paper, plastics, rubber and chemical industries said they received a surge in new orders, some of them unexpected.

Yet managers at companies that produce wood products, computers and apparel said sales and production slowed.

In any case, most economists don’t expect a sustained improvement in manufacturing until next year.

For one thing, the global economy is still soft, hurting U.S. exports. The ISM’s September export index, for example, remained under 50 for the fourth straight month.

What’s more, many businesses are awaiting the outcome of the presidential election to get a better read on future tax, spending and regulatory policies. That could keep a cap on domestic demand for manufactured goods.

U.S. outperforms

Until September’s reading, the U.S. manufacturing sector had shown slight contraction for three months in a row, the first time that’s happened since the tail end of the 2007-2009 recession

Other manufacturing sectors around the world also posted improvement in September, according to a flurry of indexes released since last Friday. Yet most were in still in negative territory, including China and the euro zone.

An index that tracks the euro-zone manufacturing sector rose slightly in September but indicated contraction for the 14th consecutive month. The gauge, produced by Markit, rose to 46.1 from 45.1 in August.

The third quarter was Europe’s worst in three years, Markit said. Read more.

In China, the world’s second largest economy, a survey compiled by HSBC remained under the key 50 benchmark for the 11th straight month. The index rose to 47.9 from 47.6. Read more.

Separately, Japan’s manufacturing index edged up to 48.0 in September from 47.7 in August.