Chancellor Bruno Kreisky of Austria was about to begin his speech to the National Press Club at 12:34 p.m. yesterday when the lights went out.

Power was off for nearly 40 minutes throughout the club-controlled 13-story office building at 14th and F streets NW, affecting not only Kreisky's speech but also transmissions from the United Press International bureau, the NBC radio network's news bureau and other news media tenants.

Elevators halted between floors, trapping occupants briefly.

The building, one of Washington's largest, is undergoing a $60 million renovation that makes much of it seem to tenants and visitors like a combat zone.

William Hickman, president of the National Press Building Corp., said engineers could not find a cause for the blackout. There was no power surge or physical disruption of electric lines, he said.

"Power would have been back on sooner except that our electrical contractor and chief engineer were in one of the elevators and were stuck," Hickman said.

In the top-floor ballroom where the Austrian leader was to speak, employes opened doors to let in natural light and then got candles for the tables. The speech went on as scheduled--without sound amplification.