Refco Inc., one of the largest independent futures trading companies in the United States, shut down one of its subsidiaries yesterday as a scandal involving its former chief executive morphed into a potentially dire cash crunch.

The New York-based firm, which trades in a variety of arcane financial products with a broad range of investors around the world, said it suspended for 15 days operations of Refco Capital Markets Ltd. Sources close to the company, who spoke on the condition of anonymity, said clients and investors sought to pull their money out of the subsidiary, draining its cash and creating what one source called "a run on the bank."

Refco on Monday said that its longtime chief executive, Phillip R. Bennett, had secretly borrowed $430 million from the company. Bennett repaid the money and was put on leave, but Wednesday federal agents arrested Bennett and charged him with securities fraud. Refco says its financial statements for the past three years, filed in August when it sold stock in an initial public offering, cannot be relied upon anymore.

Yesterday Refco said it hired former Securities and Exchange Commission chairman Arthur Levitt as well as Promontory Financial Group LLC, a consulting firm headed by former federal bank regulator Eugene A. Ludwig, which has done several investigations of large-scale corporate scandals in recent years.

Refco spokesman Rob Solomon declined to comment on whether a cash crunch was limited to Refco Capital Markets or was an indication of broader financial problems. On Tuesday, Refco said it had "adequate liquidity to run the business in the ordinary course." But yesterday it said only its regulated trading businesses had adequate capital and would keep running. Refco Capital Markets, which the company said represents a "material portion" of its business, is a wholly unregulated private market maker in foreign exchange contracts and other financial transactions conducted primarily by hedge funds, major companies and large banks both to speculate on and hedge against swings in financial markets, stocks and currencies.

Refco's larger business, its futures trading operations, is regulated by the Commodity Futures Trading Commission as well as public exchanges that engage in futures trading, such as the Chicago Mercantile Exchange.

How Refco's problems would affect the broader futures and derivatives trading markets was difficult to determine, but privately yesterday market regulators and some large traders said the firm's liquidity problems were not yet cause for broader concern.

The CFTC issued a statement last night saying it was closely examining Refco LLC, the regulated Refco subsidiary that executes trades in futures and option contracts listed on the Merc and other exchanges.

"CFTC auditors and attorneys are presently in the process of re-confirming that Refco LLC's customer funds on deposit remain uncompromised and that the capital requirements of Refco LLC are being met," the statement said.

As of Aug. 31, Refco LLC held about $4.9 billion on behalf of trading clients, according to a filing with the CFTC. That makes it among the largest regulated futures brokers, behind giant banks and Wall Street firms such as Citigroup Inc. and Goldman Sachs Group Inc.

The Federal Reserve Bank of New York is monitoring the Refco situation as part of its normal market surveillance. But the bank has not convened any special emergency meetings to discuss any possible systemic risk to financial markets.

Meanwhile, the firm's internal problems could cause Refco's trading clients to abandon the firm, leading to a potential liquidity crisis even at its regulated operations. John C. Jensen, president and founder of Heritage West Futures Inc., a California firm that executes trades through Refco, said he has not yet decided whether to take his business elsewhere. But he said he might be forced to if it appears that Refco is headed toward financial failure.

"It's getting scary because I hear that a lot of people are taking their money out, that [Refco's] stock might be delisted and that there might be cash problems," Jensen said.

Refco's former CEO, Phillip R. Bennett, is charged with securities fraud.