US STOCKS-Wall St sees worst day in a month on resources, data

* Fresh concerns over economy spark sell-off

* Lower commodity prices hit resource shares

* Goldman Sachs downgrades Wal-Mart, stock slides

* Dow off 2.1 pct, S&P off 2.4 pct; Nasdaq off 2.3 pct * For up-to-the-minute market news click [STXNEWS/US] (Updates with volume, adds details on volatility)

By Leah Schnurr

NEW YORK, June 15 (Reuters) - U.S. stocks tumbled, marking their worst slide in a month on Monday after regional manufacturing data dented optimism about the economy's health and resource shares fell alongside commodity prices.

After a series of signs the economy may be stabilizing, investors are looking for more definitive signals of its improving health. Analysts also said a pullback was unsurprising after a three-month rally.

Economists had expected to see slight improvement in the New York Fed's Empire State index, but the survey showed the factory sector shrank at a much more severe rate in June than the previous month. For details, see [ID:nN15186978].

"The bottom line is investors were starting to factor in a V-shaped recovery to the economy," said Alan Lancz, president of Alan B. Lancz & Associates Inc, in Toledo, Ohio.

"Not only do prices get ahead of themselves, but there's also a situation where if we don't get that V-shaped recovery, then you have more than just a temporary pullback. That's what might scare investors in the more immediate term."

Manufacturers' shares fell, including 3M (MMM.N), which was down 2.8 percent at $59.31, while Caterpillar (CAT.N) shed 4.3 percent to $36.12.

Oil prices fell from nearly an eight-month high after Russia expressed confidence in the U.S. dollar as the world's reserve currency, increasing the greenback's safe-haven appeal. Commodity prices and the dollar have moved inversely of late. Gains in the dollar makes oil more expensive for holders of other currencies.

Chevron (CVX.N) fell 2.2 percent to $71.08. The S&P energy index .GSPE slid 2.3 percent.

The Dow Jones industrial average .DJI fell 187.13 points, or 2.13 percent, to 8,612.13. The Standard & Poor's 500 Index .SPX lost 22.49 points, or 2.38 percent, to 923.72. The Nasdaq Composite Index .IXIC dropped 42.42 points, or 2.28 percent, to 1,816.38.

While the recent run-up in commodity prices had helped stocks extend their rally, there has also been concern that a surge in oil and other commodities could hamper any budding economic recovery. Higher energy costs are a drag on consumer spending and corporate profits.

In light volume, the indexes racked up their biggest one-day percentage loss since mid-May.