By RICHARD PÉREZ-PEÑA and MATTHEW L. WALD

Published: August 2, 2006

A smothering heat wave shattered records for electricity use across a wide swath of the country yesterday as utilities and government officials called for conservation and braced for even more strain on the power grid today.

Power systems held up well despite worries about overloaded plants, transformers or lines. But utility executives warned that the risk of breakdowns rises steadily as a heat wave wears on, and with today’s temperatures expected to top yesterday’s, with possible record highs along the East Coast, power companies were girding for a huge challenge.

Three independent system operators, agencies that manage regional grids for New York, the mid-Atlantic and the Midwest, set record highs for electricity demand yesterday, breaking records set just two weeks ago. New England was just shy of a record.

Experts say demand is rising faster than the ability to meet it, which over the long run could pose the risk of both local and regional failures.

New York City took extraordinary steps to cut consumption, including turning off the display lights on the Brooklyn Bridge and ordering the city’s jail on Rikers Island to use generators. Some leading businesses raised their thermostats after Mayor Michael R. Bloomberg ordered most city office buildings to do so.

Over all, the power grid east of the Rockies is fairly strong, experts say, in part because of changes made after the biggest blackout in North American history, in August 2003. Independent system operators and the control room engineers who monitor systems at utilities are better trained and better equipped than they were in 2003, and they are in closer touch with one another.

“At this point, everybody is on their toes,” said Stanley L. Johnson, a spokesman for the North American Electric Reliability Council, an industry group in Princeton, N.J.

As the throb of air-conditioners and generators has become the summer’s soundtrack, most striking is how fast the overall demand for power has climbed. In most cases, the system operators surpassed not only previous records, but also the predictions they made in the spring for peak summer demand.

PJM Interconnection, the system operator whose member utilities cover most of the country from the Hudson River to the Chicago area and as far south as North Carolina, oversaw delivery of about 144,000 megawatts at its peak yesterday afternoon — up more than 10,000 megawatts from the record set last summer. PJM said demand growth has been equivalent to adding another Baltimore and its suburbs each year.

The Long Island Power Authority in New York surpassed 5,600 megawatts yesterday for the first time and predicted more than 5,700 today — 10 percent higher than the record set last year. “It’s an extraordinary growth,” said Richard M. Kessel, the chairman. “This is an extraordinary event, electrically.”

The New England and New York system operators said demand could push higher today, but it was expected to drop in the Midwest. At PJM, the concern was that power use would fall in the Ohio Valley and farther west, but climb along the Eastern Seaboard, putting added strain on the major transmission lines connecting the two regions.

“Tomorrow could be tricky, because if there’s significantly higher demand in the East, getting it to the East will really tax the transmission system,” Ray Dotter, a PJM spokesman, said yesterday. “We’ll still be sweating.”

Power demand has climbed much faster than predicted across the country since 2004, raising concerns about whether efforts to build new plants and transmission lines, and encourage conservation, will satisfy the nation’s appetite for electricity.

At American Electric Power, which serves five million people in 11 states, from Virginia to Ohio to Oklahoma, J. Craig Baker, the senior vice president for regulatory services, said that the heat wave “is stressing the transmission and distribution system considerably,” and that the industry needed to think seriously about how to reinforce it.

Projecting demand for electricity can be harder than predicting the stock market, but the North American Electric Reliability Council tries to do so each spring. In 2003 and 2004, actual growth in demand was smaller than anticipated, but last year’s peak demand exceeded projections by 1.7 percent. Because growth last year was so strong, the council predicted an 0.5 percent rise this year, a number that was clearly too small.

Jim Smith, a spokesman for the New York Independent System Operator, which oversees the state’s power markets and distribution, said: “There are more people, more houses, those houses are bigger, there are more electronics in those houses, and they have bigger air-conditioning units. Computers, plasma televisions, video games, BlackBerrys, iPods — every new gadget you can think of has to be plugged in somewhere.”

More than any other factor, air-conditioning drives the increase. “When it gets hot, I don’t say, ‘I want to crank up my lights,’ ” said Jonathan Cogan, a spokesman for the Energy Information Administration, a federal agency. “What I do is turn on my air-conditioner.”

In 1978, 56 percent of American households had air-conditioning. By 2001, the most recent year for which government statistics were available, that figure had risen to 77 percent, and all evidence suggests that it has continued to climb since then.

Experts say that for now, at least, the long-distance power transmission system appears to be up to the challenge, though there is a constant threat of local distribution problems because persistent heat and the electricity surging through the lines can overwhelm equipment. That is what happened last month in parts of Queens that lost power for more than a week.

The reliability council has long advised utilities and system operators and set standards for operations and personnel training, but its recommendations were merely advisory, and investigations after the 2003 blackout showed that they were not always followed. However, on July 20, the government designated it as the electric reliability organization for the United States, a step allowed under the 2005 energy bill, making its standards mandatory nationwide.

That designation is too recent to have had any impact on reliability, industry officials said. What has made a difference, though, is a national program of audits that began after the 2003 blackout, in which teams of utility experts review one another’s training standards and operating procedures.

The audits are intended to catch problems like those in Ohio that led to the 2003 collapse across much of the Northeast, the Midwest and parts of Canada: failure to trim trees that can catch transmission lines, inadequate training of operators, and computer systems that can malfunction without humans noticing.

To deal with the latest surge in demand, power companies and government officials called on businesses and residents to cut power use voluntarily — taking steps like raising thermostats, turning out lights and drawing blinds to keep out the sun. But in some cases, conservation measures went farther. The New York Independent System Operator invoked an existing program that cuts power to some of the biggest consumers around the state, “shedding” about 600 megawatts of demand — and yet the region still peaked far above last year’s record.

Higher demand also means bigger electric bills for consumers, in part because rates rise as demand increases. Consumption also tends to rise as heat waves go on, even if the peak temperatures are no longer increasing. Nighttime temperatures stay high, so air-conditioners are used more hours each day.

As Mr. Dotter, the PJM spokesman, said, when the heat persists, people say, “I was trying to conserve but I can’t take it anymore,” and then turn up the air-conditioner.