Soaring temperatures in the upper half of the United States are creating a heavier-than-normal demand on the nation’s power resources. Usage is just shy of breaking records, but transmission grid operators say they have plans in place to deal with any unforeseen failures.

The heat wave across the Midwest, Ohio Valley, and mid-Atlantic states is expected to continue through Friday, according to the National Weather Service. In some areas, the temperature is expected to feel like 115 degrees F. Cooling is expected to start Saturday.

The extreme heat, and the subsequent reliance on air conditioning, are likely to “put a lot of strain on the grid,” says US Energy Secretary Steven Chu. The situation, Secretary Chu told reporters Thursday, has not yet reached a crisis point, but his agency is prepared to “spring into action” if blackouts occur.

“The main thing is the utility companies work with their customers and try to moderate demand, especially in the afternoon peak when [air conditioning] usage might be high,” he said.

That’s what spokesperson Paula DuPont-Kidd says her company, PJM Interconnection, will be doing if needed. The regional transmission organization is prepared to ask certain consumers, such as a local manufacturer or school system, to reduce their power load in exchange for payment.

Heat waves that last longer than a few days have the potential to stress any transmission system, and operators usually track daily weather forecasts to determine the level of power needed.

Grid operators say they are prepared for the increased demand. According to the major operators in the Northeast and Midwest, power usage this week is the highest it’s been all year, but usage is still shy of record peaks.

For instance, ISO New England, another a regional transmission organization, reached 27,550 megawatts Wednesday. The company’s record peak remains 28,130 megawatts on Aug. 2, 2006.

Only one record has been broken so far: Midwest ISO, which serves the upper Midwest through the Canadian province of Manitoba, reported that peak demand reached 103,975 megawatts Wednesday, breaking the company’s previous record of 103,246 megawatts from July 2006.

PJM, says Ms. DuPont-Kidd, will probably set a record by the end of Thursday, with an expected usage of 160,000 megawatts, breaking the record set on Aug. 2, 2006, when usage was at 158,448 megawatts. PJM operates in 13 states in the Midwest and mid-Atlantic region as well as in Washington, D.C.

The company is prepared for the increase in usage and can also tap reserve capacity, DuPont-Kidd says. “Currently everything is working the way it’s supposed to,” she says.

Utility companies are also on high alert this week. Consolidated Edison Company of New York, which serves 3.2 million customers in New York City and surrounding Westchester County, says that it expects to reach 100 percent of its projected usage amount, 13,100 megawatts, by the end of Thursday. The company’s all-time usage peak was 13,141 megawatts in August 2006.

Even though the company will be operating at peak usage Thursday and most likely through the weekend, its system is designed to accommodate up to 119 percent of demand, says John Miksad, senior vice president of electric operations.

“We don’t see capacity as an issue,” Mr. Miksad says.

Power outages were reported in the Chicago area early Thursday morning. About 73,000 homes and businesses went without power because of equipment and transformer failure, reported Commonwealth Edison.

One thing working in the favor of grid operators and utility companies is that big storms are not predicted over the next week. Thunderstorms sometimes cause a quick drop in demand (not to mention power outages), which can trigger equipment failures, says DuPont-Kidd,.

• Patrick Wall contributed to this story in New York.