New Yorkers trying to endure the blistering temperatures set a record for energy usage yesterday, even as the city is taking unprecedented steps to conserve power amid a heat wave that is expected to keep the mercury near 100 degrees through tomorrow.

From heading to the pool to buying a bottle of water or an ice cream cone on the street, city residents did everything they could to stay cool as the temperature hit 95 degrees Fahrenheit in Central Park and a record 100 degrees at La Guardia and John. F. Kennedy airports. It felt even hotter, as the heat index reached well into the triple digits, with recordings of 107 degrees in Central Park and 108 degrees at the airports, according to the National Weather Service.

Consolidated Edison reported that at 5 p.m., the power consumption reach 13,103 megawatts, topping a mark set last year of 13,059.

Despite the record demand, yesterday’s heat did not bring the widespread power outages and mass transit disruptions that accompanied last month’s heat wave. Con Edison last night reported 841 customers without power, scattered through the five boroughs and Westchester. City officials said there were no heat-related deaths.

The worst, however, may be yet to come. Forecasters are calling for temperatures between 100 and 105 degrees today, with the heat index soaring as high as 119 degrees. The temperature should return to the 80s on Friday.

Still reeling from a 10-day blackout that left more than 100,000 Queens residents without electricity, the Bloomberg administration has taken extraordinary measures to try to prevent widespread power outages this week.

Officials took major portions of the Rikers Island jail and several waste treatment plants off the power grid and put them on generators, and a litany of city landmarks were left in the dark last night. The Empire State and Chrysler buildings extinguished their spire lights, power was cut to the exterior lights on the East River bridges, and the Parks and Recreation Department turned off the decorative lights at the Coney Island Parachute Jump, Grand Army Plaza, the Washington Square Arch, and baseball stadiums in every borough.

City pools stayed open for extended hours, as did hundreds of cooling centers.

Under a heat emergency declaration signed by Mayor Bloomberg on Sunday, officials have raised the thermostat at 53 municipal buildings to 78 degrees from 72 and put dozens of elevators out of service.

The mayor is so insistent on energy conservation that he took the matter into his own hands. After spotting a running air-conditioner in a City Hall office yesterday, Mr. Bloomberg switched it off himself, he told reporters yesterday.

At an afternoon news conference at the city’s emergency operations command center in Brooklyn, Mr. Bloomberg stressed with equal vigor the importance of cutting down on power use and staying out of harm’s way. On both fronts, the message to New Yorkers was, “Take it easy.”

“It is miserably hot outside and hard on everyone,” the mayor said. “This is a very dangerous heat wave, and it is more than just uncomfortable. It can seriously threaten your lives.”

The city and Con Edison urged New Yorkers to conserve energy as much as possible by raising thermostats and turning air-conditioners off when they leave home. Mr. Bloomberg said several major companies had also agreed to reduce power consumption.

With Con Edison facing increased public scrutiny following its much-criticized response to the Queens blackout, Mr. Bloomberg was asked if he had confidence in the company this time around. “I’m confident that we will ask a lot more questions,” the mayor replied.

On the streets yesterday, the heat could be measured in several ways. The lure of ice cream was powerful, but so was the pressure to eat it rapidly. A regular-size cup of Mister Softee’s chocolate began to melt immediately upon its purchase near the Brooklyn Bridge in Lower Manhattan, where a glass thermometer recorded the temperature at 103 degrees. Within eight minutes, the soupy mess had overwhelmed the Styrofoam cup that contained it.

The heat also could be felt in the spiked sales of bottled water and other cold refreshments. The Mister Softee’s reported selling more than twice as many bottles as it does on an average summer day. A hot dog vendor on Chambers Street and West Broadway, Said Jihad, said he did even better. He estimated that he sold about 150 bottles, compared to 20 normally.

At the Jamba Juice a few blocks north, one worker said customers had bought double the number of smoothies as usual.

As hot as it was on the streets, the stuffy subway platforms below could be even more oppressive. A thermometer recorded the temperature on the downtown 2 and 3 platform as 108 degrees. At the 4, 5, and 6 train platform at the Brooklyn Bridge stop, the mercury rose to 107 degrees.

“It’s extremely hot down there,” a transit worker at the R, W station at City Hall, Jeffrey Wright, said. Mr. Wright said he took frequent breaks —admittedly more than he is allowed — and that the Metropolitan Transportation Authority provided water for employees.

A few New Yorkers did get a reprieve from this week’s heat wave, including the mascots for the city’s professional baseball teams. The Mets, the Brooklyn Cyclones, and the Staten Island Yankees were not playing at home this week, meaning Mr. Met and his colleagues did not have to suit up in their heavy costumes. (The Yankees were playing at home last night, but they have no mascot.)

“I think the people who are inside the costumes are very thankful that we have no game tonight,” a Cyclones spokesman, David Campanaro, said. Had there been a game, the mascots would still have had to work, if even for a little while, he said.

Some New York schoolchildren also were rejoicing, as the city said summer classes would be optional today.