NEW YORK (AP) _ Electrical power went out in the heart of Manhattan for half an hour Monday afternoon, trapping people in elevators, leaving shoppers in virtual darkness and halting some bond and currency trading.

The outage, which occurred on the eighth day of a heat wave that sent the thermometer to 102 degrees on Sunday, forced workers to leave the comfort of air-conditioned offices for the hot-house temperatures outside.

Con Edison spokeswoman Martha Liipfert said the power failure did not appear to be heat related. She said the outage was caused by an electrical fault at a substation at East 63rd Street.

As many as 11,000 utility customers - which can be offices or entire buildings - between 53rd and 44th streets and the East River to Fifth Avenue were affected by the outage, according to Con Edison.

The outage lasted from 1:42 p.m. to 2:15 p.m.

The Pan Am Building, Saks Fifth Avenue and the Newsweek building in the heart of the nation's biggest metropolis were in the affected area. Some traffic lights went out. But subways and most telephones were not affected and Grand Central Terminal reported no problems.

New Yorkers handled the brief outage with aplomb.

''We figured it was a power failure because of the excessive heat that has been sitting over us,'' said John Emmanuel, 44, a senior vice president at Schroeder Real Estate Association. The temperature reached 89.4 degrees on Monday after a week of 90-plus highs.

For other workers at his office building at 437 Madison Ave. the blackout came close to being something more than an inconvenience. Six people were trapped in two elevators in the 40-story tower for about 20 minutes, said firefighter John Larocchia.

At Chemical Bank on Park Avenue, traders had no access to market data, said spokeswoman Joyce Oberdorf.

''All of their screens were down so they had no market information. They could not really trade,'' she said. Lights and machines were also down at branch locations in the area, so bank customers could not make transactions.

UBS Securities Inc. suffered two outages - one when an air conditioning unit caught fire, and the second due to the power outage, said Michael Snow, senior vice president and treasurer of the Union Bank of Switzerland, its parent company.

''Basically the whole day was totally disrupted,'' Snow said. ''Trading was sort of discontinuous today.''

At the Waldorf-Astoria Hotel, a sitdown lunch for 400 guests in the Starlight Roof ''was a little bit delayed'' because of the outage, said Per Hellman, the hotel's vice president and managing director.

Liipfert said two transformers at Con Edison's East 63rd Street substation were out of service for repair earlier in the day ''when an electrical fault occurred'' at 1:42 p.m.

Big relay switches - which act like circuit breakers to stop the flow of electricity - were opened up to protect the substation from any more damage and caused the blackout, she added.

The blackout followed the hottest weekend in 14 years, with a Central Park temperature that reached 102 degrees.