U.S. stocks slid on Monday as investors fretted about the strength of an economic recovery, and falling commodity prices hit shares of energy and other natural resource companies.

Weighing on sentiment, the World Bank said prospects for the global economy remain unusually uncertain as it cut 2009 growth forecasts for most economies.

Adding to a glum economic outlook, Walgreen Co posted weak quarterly results as U.S. shoppers focused on buying only necessities. Shares in the drugstore chain fell more than 5.2 percent to $29.79.

The Dow Jones industrial average <.DJI> dropped 165.51 points, or 1.94 percent, to 8,374.22. The Standard & Poor's 500 Index <.SPX> fell 21.89 points, or 2.38 percent, to 899.34. The Nasdaq Composite Index <.IXIC> slid 49.39 points, or 2.70 percent, to 1,778.08.

When you hear the comments come out this morning downgrading global economic growth, and then some comments from Walgreen about what they are seeing on the retail side -- and they are one of the bigger drug retailers as well -- I think it gave investors a good reason to step back, said Paul Nolte, director of investments at Hinsdale Associates in Hinsdale, Illinois.

Shares of energy companies were among the biggest decliners as the front-month price of crude fell nearly 4 percent to $66.87 a barrel. Exxon Corp was down 2.2 percent to $69.48, while Chevron Corp fell 3 percent to $66.03.

Metal prices slid across the board. Shares in Freeport-McMoRan Copper & Gold Inc , which often mirror the price of gold, dropped nearly 9.4 percent to $46.15 as the precious metal hit its lowest level since mid-May.

After a sharp three-month rally, indexes have eased as traders increasingly questioned if stocks were due for a correction. Worries that the economic recovery could be tepid have wilted the optimism that drove up the S&P 500 by as much as 40 percent from the 12-year low in March. Indexes have fallen 4 percent to 5 percent since an intraday high on June 11.

On the Nasdaq, big-cap technology stocks led the decline, with Qualcomm Inc down 3.3 percent to $44.49, while Apple Inc fell nearly 2 percent to $136.81.

Apple said it had sold more than 1 million of its newest iPhone in the first three days of launch, beating expectations. The company statement also quoted Chief Executive Steve Jobs, leading at least one analyst to speculate he was back from medical leave.

(Reporting by Edward Krudy; editing by Jeffrey Benkoe)