Stocks retreated as growing concern that earnings will trail estimates at the largest American companies sent the Dow Jones Industrial Average to its biggest drop in a month.

Alcoa Inc., the first member of the Dow average to report results, declined the most in a week after sales slipped 3.2%. Monsanto Co., the largest seed producer, fell after its loss widened on lower-than-expected sales. Boeing Co. posted its steepest tumble since August after saying it needs more time to finish building its new 787 Dreamliners. The Standard & Poor’s 500 Index lost 2.68, or 0.2%, to 1,562.47 after climbing to a record Tuesday. The Dow, which also posted an all-time high yesterday, fell 85.84, or 0.6%, to 14,078.69. The Nasdaq Composite Index added 7.7, or 0.3%, to 2,811.61.

A slowdown in economic expansion may reduce profit growth at S&P 500 companies to 0.7% in the third quarter from at least 10% in each of the 20 previous quarters, according to a Bloomberg survey. Energy companies, whose shares have led this year’s rally with a 28% gain, are forecast to post a 6.6% decrease in earnings.

“It’s going to be a below-average quarter for sure,” a senior investment strategist at Trusco Capital Management in Richmond, Va., Alan Gayle, said. “We may see a little bit of softness again in the fourth quarter, softer than what the market is expecting right now.”

“The fourth-quarter earnings season is the difficult one,” the head of global strategy at Standard Life Investments Andrew Milligan, said. “If we really do see the credit market problems and U.S. housing problems causing a downturn in the U.S. economy, the fourth quarter should be the one where we really start to see some pressure.”