May 21 (Bloomberg) -- U.S. stock futures fell, signaling the Standard & Poor’s 500 Index may drop for a third day, as jobless claims topped forecasts and former Federal Reserve Chairman Alan Greenspan said the financial crisis is not over.

Wal-Mart Stores Inc., the largest U.S. private employer, and American Express Co., the third-biggest credit-card network, retreated after 631,000 Americans filed claims for unemployment insurance last week, a sign the job market continues to weaken even as the economic slump eases. Exxon Mobil Corp., the world’s largest company by market value, and ConocoPhillips declined as crude retreated.

S&P 500 futures expiring in June lost 1 percent to 891 at 8:55 a.m. in New York. Dow Jones Industrial Average futures dropped 0.9 percent to 8,319 and Nasdaq-100 Index futures declined 0.8 percent to 1,381.

U.S. stocks erased gains in the final hour of trading yesterday after minutes from the Federal Reserve’s April meeting predicted a deeper recession and American Express said growth won’t return to levels from before the downturn in the economy.

Comments from Greenspan after the close of trading yesterday suggested he sees a bigger capital shortfall in the banking system than reflected in regulators’ stress tests on the 19 biggest U.S. lenders.

‘Mortgage Crisis’

“There is still a very large unfunded capital requirement in the commercial banking system in the United States and that’s got to be funded,” Greenspan said in an interview yesterday in Washington. He also said that “until the price of homes flattens out we still have a very serious potential mortgage crisis.”

The benchmark S&P 500 has surged 34 percent since March 9 on speculation the global recession is easing. An index of U.S. leading indicators is expected to rise in April for the first time in 10 months, economists said before the report today. Other data may show manufacturing shrank at a slower pace.

U.S. stocks are at the start of a bull market that may spur an 88 percent advance in the S&P 500 in the next two or three years, Laszlo Birinyi, the founder of Westport, Connecticut- based research and money-management firm Birinyi Associates Inc. said in a Bloomberg interview yesterday.

Economist David Rosenberg said the S&P 500 may fall beneath its 12-year low on March 9 because consumer spending hasn’t shown signs of a recovery.

“We have to get confirmation the March lows are going to hold,” Rosenberg, the chief economist and strategist at Gluskin Sheff & Associates Inc. in Toronto and the former chief North American economist at Bank of America Corp., said in an interview with Bloomberg Television. “The conventional view was the November lows were going to hold. As we found out in the opening weeks of March, those lows didn’t hold.”

To contact the reporter on this story: Eric Martin in New York at emartin21@bloomberg.net.

Last Updated: May 21, 2009 08:58 EDT