Gas Explosion, Fire Cut N. Y. Power : Blackout: Hundreds of thousands are affected. A utility worker is killed after apparently rupturing a main. Scores are trapped in stalled elevators.

Hundreds of thousands of residents of Manhattan’s fashionable upper East Side and the Bronx were left without power Friday when a massive gas explosion and five-alarm fire ripped through a Consolidated Edison Co. plant, killing one person, injuring 27 others and sending a huge plume of flame and column of black smoke over the electrical facility.

Scores of people were trapped in stalled elevators in darkened high-rise apartment buildings, and the Metropolitan Museum of Art and four hospitals were forced to turn to emergency generators. Gracie Mansion, the mayor’s official residence, was darkened, as were all street and traffic lights in a 2 1/2-mile-long area of the city. Subway service was widely disrupted, and, for a time, there was no service into the Bronx, transit authority officials said.

Because of the intense heat, firefighters were forced to battle the blaze at the plant from a distance. Commuters on the nearby Triborough Bridge felt the fire’s heat in their cars. Because of the threat of secondary explosions, about 900 people were evacuated from a bus depot near the fire.

The fire first was reported at the Hellgate switching facility of Consolidated Edison Co. at 1:10 p.m. and quickly became a five-alarm blaze. Police said that a Con Ed crew was working behind the station when a gas line was ruptured. The force of the explosion hurled two workers into the East River, but they were rescued.

Police said the worker who was killed was digging a hole behind the station with a backhoe when he apparently ruptured a 26-inch gas main. The explosion gutted his vehicle.

Flames and smoke, fed by the ruptured gas line, soared 400 feet into the air. The flames easily dwarfed nearby street lights.

“It was an awesome fire,” said Fire Chief Carlos Rivera, who helped direct 250 firefighters at the scene. “It was frightening.”

“The lights dimmed really quickly, and then I heard a big blast,” said Frank Wiles, who works across the street from the plant. “ . . . You could see bricks and debris landing around the area.”

It took firemen and utility company workers more than an hour to shut down the gas main feeding the flames.

“When the valve was turned, the flames got smaller and smaller and smiles got bigger and bigger,” said Paul Laddomada, an employee of the Department of Environmental Protection.

More than four hours after the fire erupted, power began to return to some areas of Manhattan. But, as darkness fell, almost 1,000 extra policemen were sent into the Bronx to assist residents and maintain order.

Both Mayor Edward I. Koch and David N. Dinkins, who will be inaugurated as mayor on Monday, monitored the situation at City Hall.

“We have two mayors to handle it,” Koch said, as Dinkins sought to reassure New Yorkers in darkened neighborhoods that they would be secure.

After visiting the fire and returning to City Hall, where he has been mayor for a dozen years, Koch was greeted by the Police Department’s bagpipe band. The outgoing mayor grew teary eyed over the tribute as the pipes played “Auld Lang Syne.”

Utility company spokesmen said that two electrical networks were served by the equipment in the damaged plant. Power was disrupted to 77,000 customers in Manhattan and 58,000 customers in the Bronx. But these figures failed to indicate the actual numbers of people without electricity.

In some cases, a customer represented an entire apartment building, with hundreds of families.

At Con Ed’s control center in Manhattan, engineers studied the configuration of the utility’s entire electricity grid for New York City, seeking to switch power from other generating networks to the darkened areas. Con Ed said that feeder cables radiating out of the burning substation were affected by the fire.

“We turned (power) off in the west Bronx when we determined that we lost too many feeders to hold the load,” said Pat Richardi, a spokeswoman for the utility. “We acted to shut the power off. Even as we did that, Yorkville (in Manhattan) went any way as a result of not having enough feeders to carry the load because of damage from the fire.”

The power failure caused immediate problems. Police emergency service personnel rescued dozens of people from elevators. Residents rushed to local stores, buying out supplies of candles and flashlights.

“We’re in a blackout, using candles and flashlights,” said John Anderson, who lives in an apartment house on East 81st Street. “ . . . We have no water, no elevator, no furnace, no nothing.”

In a nearby food store, Ann Chang was unable to make sales when her electric scales and cash registers stopped working.

At the Crystal Aquarium on 3rd Avenue, where tropical fish swim in dozens of tanks, Victor Hritz, an employee, said he had made contingency plans before electricity was restored to bring in a portable generator and a kerosene heater to save the store’s $35,000 inventory of fish. He carefully monitored the water temperature in the tanks.

“Once it goes below 70 degrees, you’re in trouble,” Hritz said. “The fish can die of shock . . . .”