If America is required to march off once again to the moral equivalent of war, as President Carter once called his energy conservation program, at least it's better prepared to fight.

The nation is getting much more bang out of every barrel of oil it burns than it did in 1973. The difference is this: If the United States were using oil no more efficiently now than it was 17 years ago, it would need about 52 percent more oil than it uses to sustain today's economy, according to the Department of Energy.

The oil price spikes of 1973 and 1979 have succeeded in building a measure of energy conservation into the fabric of American life, although some of it has unraveled in recent years as the price of oil stabilized.

"I'd hate to tell you the number of computers and CD players that are plugged into this house," said Stephanie Rapp of Glenview, Ill., a Chicago suburb. In 1979, Rapp and her husband were sufficiently concerned about the nation's energy crisis to spend a week trying to live with as little electricity and gasoline as possible. They turned down the refrigerator and the hot water heater and left the lights off after the sun set. They cooked on an outdoor grill and rode bicycles to work.

Now, like many other Americans, the Rapps in some respects are more energy complacent, but in other ways they still are conserving.

When they turned the lights back on after the 1979 experiment, the Rapps replaced many of their light bulbs with lower-watt bulbs, which they still have. And when they bought new kitchen appliances, they looked for the most energy-efficient stove and refrigerator they could find. They never replaced the electric can opener and the food processor that they gave up in 1979. But they did replace draperies with pleated blinds made out of a double thickness of fabric to help insulate the house.

The Rapps' push for energy efficiency was part of a national downshift in energy consumption in the last two decades that has only recently begun to be reversed. As a result, total energy consumption today is not much higher than it was in 1973, even though the economy now is almost twice as big.

Some of the changes have been striking:

From 1972 to 1986, the amount of all kinds of energy used to produce a dollar of gross national product declined 26 percent, and only Japan has outpaced the United States in increases in energy efficiency gains per unit of gross domestic product.

Auto fuel efficiency has increased 78.5 percent since 1975, from an average of 15.8 miles per gallon to 28.2 miles per gallon.

Houses built today are 50 percent more energy-efficient than houses built in 1973. Freezers are 77 percent more energy efficient.

Spending on oil for utilities and transportation dropped to an average of 4.1 percent of a family's expenditures in 1988 from 5.4 percent in 1972-1973, according to the Bureau of Labor Statistics.

But as oil prices stabilized in the 1980s, the social and political climate changed. The Reagan administration backed away from many of the energy conservation measures enacted in the past.

"{President} Reagan's attempts to abolish the Department of Energy and to cut support for research and development programs in energy efficiency sent a very loud and clear message to the American people that energy conservation was no longer a very important concern," said James Wolf, executive director of the Alliance to Save Energy, a Washington-based energy conservation group.

Whether the signals came from the Reagan and Bush administrations, as consumer groups and environmentalists charge, or whether they came from the prices posted on gasoline pumps, the public was clearly receptive.

Americans began to abandon smaller cars for high-energy consuming minivans, pickup trucks and four-wheel-drive vehicles such as Jeeps. "Our Ford Explorers are gangbusters," said Jerry C. Cohen, owner of Jerry's Ford and two other Washington area dealerships. "We're selling every Explorer we can get in, and what we can't get, we're begging Ford to send us more."

The Explorer is a sport-utility vehicle that averages about 17 miles per gallon, 11 miles per gallon less than cars in general.

Automobile fuel efficiency, which had been making big gains since 1973, began to level off in 1986 and declined in 1988 and 1989.

A Department of Energy report on energy conservation trends found that the average efficiency of new products, including automobiles and appliances, bought in 1988 and 1989 "has leveled off or fallen for the first time in more than a decade."

Autos are one of the few remaining areas where researchers expect any significant conservation gains. "The opportunities for further oil reduction are very, very limited and they largely show up in transportation efficiency," said Barry McNutt, of the Energy Department's Office of Policy Planning and Analysis.

The Bush administration has proposed a small increase in federal standards for auto mileage, but it has resisted legislation introduced in Congress calling for automakers to make sharper improvements in the fuel efficiency of their cars.

With the crisis in the Middle East driving oil prices back up, the push for energy efficiency is expected to regain momentum. But observers believe that it is not likely to follow the pattern of the 1970s, when the first response to energy shortages was to turn down thermostats and drive less. Those responses created no legacy of conservation because they called for personal sacrifice, many experts said.

"It's a sort of unfortunate backlash that has happened -- that energy conservation was equated with freezing in the dark," said Robert K. Watson, an energy resource specialist for the Natural Resources Defense Council. "Unfortunately people are not willing to give up amenities right now. They're going to force our kids to do that."

What people are willing to do is make investments in energy efficiency that will save them money in the future.

Conservation could get another boost as recent concerns about global warming focus attention on reducing carbon dioxide emissions -- another byproduct of reducing energy use. The environmental concerns may give added impetus to the push for energy conservation, said Alan Miller, executive director of the Center for Global Change at the University of Maryland.

Many states have been particularly aggressive in promoting and developing energy efficiency and in funding research into alternative energy sources than the federal government has been, and state energy officials said they expect the Persian Gulf crisis to increase those efforts.

"We hope this is more than a warning," said Mark Ginsberg, director of the Arizona Energy Office. Arizona has spent $500 million on energy projects, including a 4,000-home solar development on state land.

"We should have learned our lesson in 1973 and 1979," he said, when anticipated shortages led to allocation, price controls, gasoline lines and economic disruption. "I hope, without the same consequences, this might be a wake-up call."

Staff writers Spencer Hsu, Dana Priest and Cindy Skrzycki contributed to this report.