Stock futures dropped on Wednesday as investors turned cautious about the outlook for profits after Alcoa Inc's earnings missed estimates and International Paper Co. issued a profit warning.

Investors hoped third-quarter earnings would start on a firm footing to ease concerns about the toll of the housing slump on the economy.

But Alcoa's results, released after the bell on Tuesday, and profit warnings from companies, including oil producer Chevron Corp. and leading refiner Valero Energy Corp tempered optimism.

You're seeing a bit of caution before a long list of earnings begin to pour in, said Peter Cardillo, chief market economist at Avalon Partners.

The market could run into some trouble here short-term as some of the earnings could come in somewhat less than expected. There are going to be some upside surprises but I think there will be more downside surprises.

Disappointment with profits could trigger a 3 percent to 5 percent pullback in the stock market, he added.

S&P 500 futures fell 4.4 points, and were about even with fair value, a mathematical formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract.

Dow Jones industrial average futures slipped 28 points, and Nasdaq 100 futures dropped 4.5 points.

Valero Energy shares fell more than 3 percent to $69.75 before the bell following the company's profit warning that third-quarter profit would be below Wall Street's estimates.

International Paper blamed weak land sales for its profit warning, while both Chevron and Valero Energy cited weak refining margins, among other factors.

But shares of Costco Wholesale Corp, the No. 1 U.S. warehouse club operator, rose 1.4 percent to $64.20 before the bell after the retailer posted a higher profit on strong sales.

Companies also due to post results on Wednesday, include Monsanto Co, Progressive Corp and Ruby Tuesday Inc.

The Dow and S&P 500 jumped to close at record highs on Tuesday after minutes from the Federal Reserve's last meeting showed inflation expectations were contained, leaving open the question of whether another rate cut is near.

According to Reuters Estimates, S&P 500 third-quarter earnings are projected to rise 3.2 percent compared with a year ago. The health-care and technology sectors are expected to show the largest gains.