Even in shorts and a T-shirt, the general coordinator of the Park Slope Food Coop, Joseph Holtz, had a rim of sweat around his head yesterday. It was the heat, of course, but it also was the frantic process of reopening the Coop after it had been closed for 17 hours because of a power outage along Union Street.

“We hardly ever close,” he said as about 40 Coop workers rushed around the store to get it open for the evening rush. “Even during the 2003 blackout we weren’t closed this long.”

At about 8:30 p.m. on Monday, the lights in the store started flickering. Then they went out, the result of a fire below street level caused by the excessive heat conditions, Consolidated Edison officials said. More than 100 people were in the store at the time, but no one could leave with their groceries because the cash registers and the phones were not working, either.

“Abandoned shopping carts with food were all over the store,” another coordinator at the store, Jessica Robinson, said.

Like most in the city, though, the Coop dealt with it. It gave away much of its perishable produce to City Harvest, Christian Health in Park Slope, and other benevolence organizations. Mr. Holtz said the Coop would lose a few thousand dollars because of the outage, but it was open again for the evening rush.

The two-avenue block along Union Street was just one of many outages across the city. Areas in northern Queens were hit hardest, Consolidated Edison officials said. As of yesterday evening, more than 700 homes and businesses were without electricity citywide. More than 40 people had been admitted to hospitals because of heat-related illness, a spokesman for the city’s Office of Emergency Management, Jarrod Bernstein, said.

The thermometer in Central Park hit 95 degrees at about 2 p.m. yesterday, a National Weather Service meteorologist, John Murray, said.With the humidity, it felt like 99 degrees, he said. It was a cruel kind of heat that made use of the same kind of humidity that would chill a person to the bone during winter. It snaked under clothing, into subway tunnels and trains, and somehow even infiltrated the shade. Still, it was no match for the city’s highest recorded temperature for the day, when it hit 101 degrees in Central Park in 1951.

A hot dog vendor at 60th Street and Fifth Avenue, Saam Salan, said he had sold 24 bottles of water at $2 each in a matter of hours.

“Of course, it’s the heat,” he said.

The entire Seventh Avenue subway line, which reaches as far as the city’s border with Westchester in the Bronx and Brooklyn College in Flatbush, shut down at the height of rush hour in the morning. Transit officials were investigating whether heat caused the signaling system to malfunction, a spokesman, Charles Seaton, said. With power especially affected in Queens, the no. 7 line was running local because of low voltage in the electrified third rail.

Three of the eight feeder cables that send electricity to La Guardia airport also shut down, leaving the west side of the airport without air conditioning, lights, or a working baggage claim service. Thirteen American Airlines flights and four Delta Air Lines flights were canceled, and others were diverted to John F. Kennedy and Newark airports, airline officials said. Emergency generators powered some dim lights in corridors of the airport until electricity was restored.

Mayor Bloomberg and Consolidated Edison officials asked that city residents minimize their electricity use so that the sporadic power outages could be addressed and the city be returned to a state of evenly air-conditioned normalcy. Some lights were turned off at City Hall at the mayor’s request.

“In the end, the solution is in the hands of all of us,” he said.

Meanwhile, ice cream at a Cold Stone Creamery at 31st Street and Ditmars Boulevard was quickly softening.

“It’s melting. It’s like soup,” a cashier, Michelle Suarez, 17, a drama student at Long Island City’s Frank Sinatra School of the Arts, said. “You can’t walk a centimeter without sweating.”

The power suddenly went off on the block in Astoria at about 1:30 p.m. The six young women behind the counter were fanning themselves, and contemplating closing the shop early. A nearby bank and a cell phone store also were without power, and manhole covers shot into the air along a stretch of 30th Avenue.

The City Council member for the area, Peter Vallone Jr., received more than 20 calls from concerned residents, he said.

“This happens at the tail end of a heat wave,” he said. “It’s the equipment. It’s old.”

One of the coolest places in the city — a destination that people more likely happened upon than sought out — was the penguin room at the Central Park Zoo, a spokeswoman, Kate McIntyre, said.

“Everyone’s been hanging out there lately,” she said.

The temperature in the viewing room is 55 degrees, and the penguins stand on view in 36 degrees of cool.