A COMMITTEE of the National Academy of Sciences recently concluded that in the year 2010 "very similar conditions of habitat, transportation, and other amenities" could be had in this country from an economy that consumed - pay attention here - either twice as much energy as we do today, or 20 percent less. Translated from the academy's solemn prose, this remarkable assertion apparently means that we have a choice between enjoying the same lifestyle - goods, services and total economic activity - fueled by the equivalent of either some 70 million barrels a day of oil - or 30 million barrels. The difference comes from conservation.

Ever since the first oil shock of 1973, a number of voices have been touting the potential fo conservation as a primary energy source for the United States. Generally, they have been discounted as obsessive environmentalists - or some other form of vague romantic. Now, however, the Harvard Business School - untinged by any hint of no-growth bias - adds its voice to the chorus with the release of its six-year study, which concludes that energy conservation is the country's largest energy resource for the next decade. Indeed, the business professors, of all unlikely men, conclude that conservation, coupled with relatively modest new production incentives, is not only the best, but also the most politically acceptable energy plan.

What does this mean for the average American who three days from now must begin to abide by the government's first major conservation initiative, mandatory thermostat settings? Does a conservation policy mean that Americans must accustom themselves to ever and ever less comfort and convenience, on a downward descending curve to steamy summers and glacial winters? Will conservation solve our energy problems by taking us all back to the cave?

The answer, according to the best experts, is no. There is, they say, a wide array of conservation possibilites that can both save large amounts of energy (a barrel saved is a barrel not imported) and do it without slowing down, heating up, frustrating or in some other way cramping the style of the American consumer. The possibilities range from higher mileage standards for cars and trucks, to more energy-efficient building design and retrofit of existing buildings, to letting factories that need steam share the same site as power plants, which make steam as a waste product from making electricity (known as "cogeneration" to the trade, this is common practice in Europe).

Most such changes have this in common: They require changes in our institutions - governments regulations, industrial practices, building design, etc. - but, unlike the thermostat-setting rule, they do not directly affect the consumer's daily routine. The family that purchases a new appliance that meets more exacting efficiency standards and thereby saves energy can only be expected to be pleased.

This is not to dismiss the value of measures like the pending thermostat requirements. Any savings, in the current situation, will help. But the growing opinion amony energy analysts is not just that conservation is a vital energy resource that should be tapped, but - more interestingly - that the steps which promise the largest return are those requiring institutional, not personal change.