NEW YORK (AP) _ One Wall Street firm moved its trading operations to a hotel ballroom and another rented a fleet of portable toilets Tuesday as a chunk of Wall Street remained without power due to a freak blackout.

Securities industry executives said some firms had to shut down at least temporarily and faced mounting losses because of the power outage that hit early Monday afternoon when an electric company substation caught fire.

Power was restored to most of the Wall Street area and the American Stock Exchange and New York commodities markets, which reopened Tuesday morning.

But other large firms ran on emergency generators or dispatched traders to offices at other firms that offered help. Nomura Securities International Inc. scattered its employees around the city, according to people who work on Wall Street.

Bill Murphy, a spokesman for Consolidated Edison Co. of New York, said the utility expects to restore power fully to the area by Monday. Some customers could have power by Thursday, he said.

The blackout trapped thousands of workers in un-airconditioned, glass towers on a steamy Monday.

County Natwest USA shifted the 75 people in its equity sales and trading operations to the Grand Renaissance ballroom at the Helmsley Palace hotel in midtown Manhattan after it was driven from its offices at 100 Wall Street.

Employees of Quick & Reilly Inc. hauled trading and account records down 14 flights of stairs and into the nearby offices of its stock clearing firm. The discount broker managed to hook up telephones shortly after the market opened at 9:30 a.m.

''We all came down carrying boxes and bags,'' said Thomas Quick, the brokerage's president. ''Then it was navigating the crowds on the streets.''

Reuters Holdings PLC said its foreign exchange trading and market information services were inoperative in sections of the Wall Street area until a backup generator was activated at its data service center late in the trading day.

Cowen & Co., a trading firm, ran on a diesel-powered generator it installed on the roof nearly three years ago for $500,000.

''I think we'd be out of business right now if we haven't made that decision,'' said Creighton Peet, Cowen administrative partner. ''I know some other firms that are in real trouble right now.''

The firm, located on the East River near the South Street Seaport market, was without water and toilets for about 600 employees. Cowen has filled its 5,000-gallon diesel tank twice and rented 20 portable toilets for the week at a cost of $2,000, Peet said.

J. P Morgan Securities Inc., with about 800 employees, operated on backup generators and routed power to priority trading departments. Some workers were given the day off and ''lots of other functions aren't being staffed,'' spokesman Joe Evangelisti said.

He said there was ''minimum lighting'' on the firm's floors at 60 Wall Street, while ''copy machines are out, fax machines are out.''

''We're trying to make it so that clients don't realize there's anything wrong,'' Evangelisti said.

While larger firms were able to turn to backup generators, smaller operations had to move to other quarters. Phone service was disrupted in part of the blacked-out area.

Discount Corp. of New York, primary dealer of U.S. government securities, shifted key traders and salespeople to emergency offices rented in Jersey City, N.J., across the Hudson River, vice presdent Phebe Miller said. She said the firm was operating on backup computers.

''We tried to get in at the crack of dawn and weren't allowed access to the building,'' said Tom DiVuolo, a fund administrator with Kenmar Avisory Corp., a 20-person money management firm that relocated to its computer operation facility in Plainview on Long Island.