(Bloomberg News) 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.

MF Global, the holding company for the broker-dealer run by former New Jersey Governor and ex-Goldman Sachs Group Inc. Co- Chairman Jon Corzine, told regulators yesterday about deficiencies in accounts that it managed for clients in the futures market, the CFTC and Securities and Exchange Commission said in an e-mailed statement.

Corzine, 64, now faces a regulatory probe as well as a bankruptcy. He wagered $6.3 billion of the firm's own money on sovereign European debt in a bid to increase profits. Instead, the firm reported a $191.6 million quarterly loss on Oct. 25 as Europe's debt crisis led to demands from regulators to boost capital, as well as credit downgrades and margin calls, MF Global President Bradley Abelow said.

Under CFTC regulations, futures brokers that trade on exchanges are required to keep their clients' collateral, often cash or securities, separate from their own accounts. The segregated collateral is meant to reduce risk in futures trades. MF Global had almost $7.3 billion in customer funds in segregated accounts as of Aug. 31, according to the most recent CFTC data.

'Third Rail'

"It's kind of considered the third rail of the brokerage industry that when you're holding your customers' funds in their names, you don't touch them -- even in an emergency situation when you're running short of cash," Darrell Duffie, a professor at Stanford University's Graduate School of Business, said in a telephone interview.

When accounts don't add up, "there is a whole range of possibilities, everywhere from an accounting error, to a technical glitch, and, of course, one can't rule out misbehavior as a possibility," Duffie said.

Corzine and Diana Desocio, an MF Global spokeswoman, didn't respond to e-mails or phone messages seeking comment.

The regulators said in their statement they advised bankruptcy as the "safest and most prudent course of action to protect customer accounts and assets."