Gas prices finally headed down last week, and may have peaked for the year, the Energy Department reported. This is good news for drivers and businesses. But the pattern over the last 30 years suggests that this is bad news for anyone who believes that Americans, the world’s biggest oil consumers, can ever curb their energy consumption.

For all the scolding about America’s energy gluttony, and for all the warnings about foreign entanglements linked to oil addiction, price seems to be the only factor that moves people to change habits.

Consider the Toyota Prius, whose gas-electric hybrid engine gets upward of 60 miles a gallon. Only after gas prices rose to 21-year highs earlier this year did its sales surge, up 100 percent this year over last.

The Prius is hip, for the moment. But, then, so was the Ford Escort and even the lowly Yugo, a pair of gas-efficient cars that had their brief shots at fame when the Persian Gulf tumult more than two decades ago drove up prices.

In the long term, the record shows that Americans will not give up their big cars. And polls show that a majority of Americans say they will use less energy only if it is easy to do so. That is, we will use less energy only if there is a nearly painless way to do it.

Even if Americans could curb demand, there are plenty of people who think energy efficiency by itself will not curb the need for huge new production. The Bush administration says that even with conservation, a new power plant will have to be built every week to meet an estimated 29 percent rise in demand by 2020.

But critics of the administration argue that conservation should be given a chance, either with carrots or sticks. And an emerging school of thought sees technology, coupled with price incentives, as a way for energy conservation to break the old mold of ever-increasing demand.

“Fortunately for us, technology can solve a lot of these problems,” said Kateri Callahan, director of the Alliance to Save Energy, a nonprofit group of government and industry officials.

The conservation side points to the example of the 1987 law signed by President Ronald Reagan forcing manufacturers to make energy-efficient appliances.

As a result, household energy use has fallen because of power-efficient appliances and technology-smart homes prodded along by tight new building codes. The average refrigerator uses a third less power than it did 15 years ago.

The fact that most air conditioners, refrigerators, ovens and water heaters do the same job with less power is one big reason why per capita energy use has remained about the same over the last 20 years, according to the Energy Department, while overall use has risen with a swelling population and less-gas-efficient vehicles.

“Americans will always follow the money,” said Susan Kennedy, a California public utilities commissioner who helped fashion a conservation program that has made her state the nation’s most energy-efficient. “Incentives have to be there.”

Today, owners of hybrids receive a federal tax break, a $1,500 deduction this year. And hybrids are popular in Virginia partly because they are allowed in the car-pool lane even if the driver is alone in the vehicle.

But hybrid sales are still a fraction of all car sales, and Americans still use 10 times more gasoline per capita than the world average, according to the World Resources Institute. Even in wide-open Australia, people use 45 percent less gas than Americans.

Conservation groups want the government to do more. Current federal requirements have broad loopholes for trucks and S.U.V.’s, and for cars that burn a small percentage of ethanol, even if they run on gasoline all the time.

The big automakers have fought higher fuel-economy standards. They argue that consumers don’t want to drive lighter, smaller cars, and that any new standards would slow a powerful sector of the economy.

Rising gas prices are supposed to help curb energy consumption. As soon as gas reaches something like $3 a gallon in the United States, hybrids will move beyond the asterisk phase, people in the car industry say.

Even at $2.50 a gallon, gas is cheap by historical standards. Paul Taylor, the chief economist at the National Automobile Dealers Association, said a 50-cent-a-gallon increase is still only a $300-a-year hit on the average driver – not enough to prompt a divorce from the gas guzzler.

William C. Ford Jr., the president of Ford, has said that higher gas taxes are needed to change consumer choices substantially. But few politicians want to lead the way. Senator John Kerry is paying the price for even considering higher gas taxes years ago; a Bush campaign ad lashed him for what it called this “wacky idea.”

Americans have cut energy use during times of crisis. After the Arab oil embargo in the 1970’s, petroleum consumption in the United States dropped substantially. And in the summer of 2001, Californians, facing months of blackouts, slashed their energy demand. They were rewarded: by reducing the use of power by 20 percent, consumers could get a 20 percent break on their utility bills.

Since then, even with the incentive no longer in place and a fast-growing population, California has significantly modified the way it uses power, cutting consumption by 10 percent or more over the last three years.

“We may be the most energy-efficient place in the world now,” Ms. Kennedy said. “The key was getting people to make permanent changes. Instead of just turning off the lights, we needed them to change the kind of light bulb they used.”

But if history is a guide, that won’t last long. After the energy crises ebbed in the 70’s, consumption gradually rose and took off in the 90’s.

In his new book, “The End of Oil,” Paul Roberts says conservation in the 1970’s and 80’s, by driving down energy prices, had the unintended effect of taking away incentives to use less.

“Paradoxically, conservation’s great success was also its downfall,” Mr. Roberts wrote. “As oil prices fell to $10 a barrel, few Western consumers saw any reason to continue conserving.”

Maybe being hip will help the cause of conservation, which has had an image problem ever since Jimmy Carter put on a sweater and urged people to turn down the heat.

The Republican Party’s rising star, Gov. Arnold Schwarzenegger of California, is urging drivers and home owners to use less energy, in ways big and small. He has tied energy conservation to body-building, with a program called “Flex Your Power at the Pump,” and wants to see hydrogen stations at regular intervals along California’s freeways.

Of course, Mr. Schwarzenegger still owns three Hummers, which average about 12 miles to the gallon. But he has put one of them in storage and is converting another to hydrogen fuel cell power.

Still, it’s hard to imagine him driving a Prius.