A government order expired Tuesday that temporarily banned a certain kind of short selling of the stocks of mortgage- finance companies...

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WASHINGTON — A government order expired Tuesday that temporarily banned a certain kind of short selling of the stocks of mortgage-

finance companies Fannie Mae and Freddie Mac and 17 large investment banks.

The companies’ shares have stabilized since the ban took effect July 21. The Securities and Exchange Commission says its order helped prevent stock manipulation, and that regulators will be able to analyze data to gauge its effectiveness. But some experts say that may be difficult to determine.

The SEC instituted the emergency ban last month after a precipitous slide in the shares of Fannie and Freddie, the government-sponsored companies that together hold or guarantee more than $5 trillion in home mortgages — nearly half the U.S. total.

The agency plans to consider new rules meant to provide additional protections against abusive “naked” short selling in the broader market of public companies, while allowing legitimate short selling.

That prospect has raised concern among advocates for hedge funds and private investment companies, which protested the SEC’s extension of its order.

“What is … more significant is what long-term rules the SEC plans to propose,” said Gary Distell, a partner in the financial-services practice at law firm Katten Muchin Rosenman in New York.

Expanding the order into a marketwide rule “would force firms to spend money to automate their systems and would add costs to both brokers and customers in the form of increased borrowers’ fees,” said Distell, who formerly was an attorney at the now-defunct investment firm Bear, Stearns & Co. “In this time of economic uncertainty, that would not be a popular outcome for Wall Street.”

Short sellers bet that a stock’s price will fall so that they can profit from it. They borrow shares of the stock and sell them. If the price drops, they buy cheaper actual shares to cover the borrowed ones, pocketing the difference.

“Naked” short selling occurs when sellers don’t even borrow the shares before selling them, and then look to cover positions immediately after the sale. The SEC’s temporary order required short sellers to actually borrow shares before selling them.