Most of suburban Washington, with its energy-wasting sprawl, looks like it was designed by planners from OPEC. But one intersting exception is emerging in Reston, the new town that has been building for 15 years on an old dairy farm east of Dulles International Airport. Though not long ago it was a convenient citation for why new towns were impractical dreams, Reston today is offering some quite down-to-earth examples of how significant energy conservation can be achieved.

Of all the statistics, perhaps the most interesting is the one on jobs. There are 10,000 jobs in Reston, and 40 percent are held by people who live in the town. Even if those 4,000 take cars to work, as most do, they use only a fraction of the gasoline consumed by the typical suburban commuter.

Many residents, of course, work in the Washington area. But 1,400 of those long-distance commuters use Metrobuses leased by the volunteer-created Reston Commuter Bus service to get to their jobs. That means that Reston, whose 32,000 residents make up only 5 percent of Fairfax County's population, is providing more than 10 percent of the count's total bus passengers.

Within Reston, 500 people daily are going to dentists, grocery stores and flute lessons via the Reston Internal Bus Service, which costs kids a dime and adults a quarter. The system was designed for 300 people.

No one has estimated how many barrels of oil are saved because of Reston's design, which incorporates a number of features that are anathema to the typical suburb. The clustering of residences results in fewer miles traveled by car, the closeness of may residences to shopping areas reduces the total number of trips Its insistence on saving trees means that air conditioners don't have to work so much in the summer. A high percentage of townhouses and condominiums means that many dwellings can be heated and cooled more efficiently than single-family houses, which account for more than 70 percent of the development in Fairfax County outside of Reston.

Then there are Reston's recreational facilities, which, because they are scattered throughout neighborhoods, are within biking and even walking distance of most residents. No one has calculated how many of Reston's residents have opted to spend their weekends at the 12 town pools and 30 tennis courts instead of guzzling out to Ocean City or Virginia Beach, but don't count on finding an open lap lane or court.

When Reston was conceived by Robert E. Simon Jr. in the early 1960s, no one seems to have foreseen an energy crisis serious enough to require people to ask themselves "is this car trip necessary?" Perhaps that's why Reston for so long seemed like a well-intentioned but impractical dream. But now most of us calculate miles as diligently as dieters calculate calories.

Yet for all its acheivements in energy conservations, Reston is not likely to be confused with Davis Calif., where public and private resources have combined on a systematic and wide ranging program involving recycling, a building code that encourages solar orientation of houses and even a farmers' market.

In at least two major areas, Reston has a lot of slack to take up.

One is conservation in housing, something that has attracted the interst of home buyers the way compact cars have won over motorists.

Reston's undeveloped land is owned by a big oil company -- Mobil -- which likes to lecture Americans on the need for energy conservation. But Mobil has shown no inclination to get involved in any significant energy-saving experiments in new housing. It is staying out of construction altogether. Gulf Oil, which sold that part of Reston to Mobil, didn't get involved in such experiments either.

What few conservation experiments are taking place in Reston are the work of individual entreprenuers. Architect-developer Michael Oxman, for instance, will soon start building 55 houses that will make aesthetics and conservation work together. His houses will offer, as an option, a heat pump that extracts heat from water instead of air. Oxman's pumps will draw heat from water even when there is a layer of ice on the pond. They will work when the air temperatures goes down to zero degrees. The pond will be replenished in part by underground water drawn up by a windmill, which Oxman is incorporating into the design of his project.

A second conservation area in which it falls short is local commuting. Reston has done little to make it more inviting for in-town workers to leave their cars at home and commute by bicycle. The 37 miles of walkways get people to pools, tennis courts and shops, but rarely to their jobs.

But what is finally remarkable about most of Reston's energy conservation is that it was unintentional. Simon wanted people close to their jobs so they would have more time for the good life. The trees were saved because they were pretty and a buffer against noise.

What would Reston -- or, for that matter, any other large-scale development -- achieve if conservation were a policy as well as a happy accident?