U.S. stocks slumped on concern that a Greece referendum pledged by Prime Minister George Papandreou may threaten Europe’s bailout. Papandreou’s gambit risks pushing the country into default if rejected by voters, and raises the ante with dissidents in his own party. Equity futures extended losses after state-run Athens News Agency reported that six senior members of the ruling party called on Papandreou to step down. Papandreou will brief German Chancellor Angela Merkel, France’s President Nicolas Sarkozy and the heads of the European Central Bank and International Monetary Fund on developments in Greece in Cannes tomorrow, on the sidelines of a meeting of Group of 20 countries. Merkel and Sarkozy called for the implementation of a European deal to write down Greece’s debt.

Stocks also fell after data showed a Chinese manufacturing index dropped to the lowest level since February 2009. In the U.S., manufacturing grew less than forecast in October, depressed by a drop in inventories that may set U.S. factories up for stronger growth heading into 2012.

U.S. regulators are investigating whether hundreds of millions of dollars are missing from client accounts at MF Global Holdings Ltd., according to two people with knowledge of the matter. The firm, which filed for bankruptcy protection yesterday, was ordered by the enforcement division of the Commodity Futures Trading Commission to preserve records for the review, one of the people said.

Dow 11,694.78 -260.23 -2.18%, Nasdaq 2,613.30 -71.11 -2.65%, S&P 500 1,222.57 -30.73 -2.45%

All 10 groups in the S&P 500 fell as financial and commodity shares had the biggest declines. Morgan Stanley and Citigroup Inc. retreated more than 7.2 percent as a gauge of European lenders tumbled 6.7 percent.

Alcoa Inc. (AA), Boeing Co. (BA) and Cisco Systems Inc. (CSCO) decreased at least 3.4 percent, pacing losses among companies most-dependent on economic growth.

Baker Hughes tumbled 8.6 percent to $52.99. The oilfield contractor reported third-quarter earnings excluding some items of $1.18 a share, missing the analyst estimate.