Shares of Alcoa slid 4.7 percent to $8.70 and weighed on the Dow following the U.S. aluminum producer's report late Tuesday of a quarterly net loss. Alcoa attributed the loss to a slump in the price of aluminum and weak demand. On Wednesday, a Nomura analyst cut the target price on Alcoa's stock to $9 from $12, citing "continued weakness in aluminum prices" as a key reason for the change.

Chevron Corp shares fell 4.2 percent to $112.39 and ranked as the biggest drag on the S&P 500 after the second-largest U.S. oil company warned that third-quarter profits would be "substantially lower" than in the previous quarter. Chevron said a hurricane and planned maintenance had curtailed its oil and gas output, while a fire hurt its refining business.

An S&P energy sector index fell 1.9 percent.

The S&P 500 index is on track for its fourth day of declines on worries that the global economic slowdown will hurt profits more than expected. S&P 500 companies' third-quarter earnings are expected to fall 2.9 percent from a year ago, which would be the first decline in three years.

"The temptation to sell is out there," said John Brady, managing director of R.J. O'Brien & Associates in Chicago. "Equities have had a tremendous year, and the outlook is very unclear. So why not reduce risk? It's hard to imagine an additional 20 percent rally from here in the next three or four months."

The larger economic backdrop is also casting a shadow. The International Monetary Fund and the World Bank recently cut their global outlooks. And the European debt crisis drags on.

With the latest decline, the S&P 500 broke below the technical support level of 1,440.

"We think we will tuck under 1,400 but I'm not calling for a wholesale sell-off," said Rick Bensignor, senior trading strategist at Wells Fargo Securities in New York. "We're still not far off the highs, and have not yet seen significant distribution panic selling of stock."

The Dow Jones industrial average dropped 103.65 points, or 0.77 percent, to 13,369.88. The Standard & Poor's 500 Index fell 8.45 points, or 0.59 percent, to 1,433.03. The Nasdaq Composite Index slipped 13.43 points, or 0.44 percent, to 3,051.59.

FedEx Corp said it plans to cut costs at its underperforming express air freight and services divisions, with a goal of improving profits at those operations by $1.7 billion over the next four years. FedEx shares gained 4.7 percent to $89.57.

The cautious outlooks are the latest in a string of forecasts from large multinational companies, including Caterpillar Inc and Hewlett-Packard Co .

(Editing by Jan Paschal)