Let's hear it for Osbourn High -- the school in Manassas that told its students to stop driving their cars to school. The crowded parking lots around the high schools are among the most conspicuous examples of wasted gasoline, since a school bus stops near the home of each of those children twice a day. Osbourn High gives exemptions to students who need cars to get to jobs. But the number of students' cars was down, in the first few days of school, by two-thirds. Whether this sensible and public-spirited rule will stick depends on public support.

Public support for gasoline conservation seems to be fading. Several northeastern states have now happily lifted the odd-even laws that restricted each car to alternate days at the pump. These laws remain technically in force in this area, but they are not much observed. You can already hear the murmur: things have returned to normal, so why not abandon all the harassments of conservation?

The reason is that things haven't returned to normal. The gasoline lines are mostly gone -- but it's only because motorists are driving less than they did a year ago. If people were to begin using their cars again as they did last year, the lines would immediately reappear.

Last month the country's gasoline supply was around 300 million gallons a day. A year earlier it had been 9 percent higher -- almost 330 million gallons a day. Since then, the number of drivers and cars has grown. The country is now at least 10 percent short of the flow of gasoline it would need to let everyone go back to last year's habits.

Demand is still held down by the memory of the lines last May and June. For another thing, the price has risen about 20 cents a gallon since early spring. Despite all the assertions to the contrary, people demonstrably use less when it costs more. Equally important, it's hard to find gasoline at certain times of the day and week. Not many filling stations have been open on Sundays. Very few are open after dark.

Students at Osbourn High -- one explained -- consider it "cool" to drive instead of taking the school bus. Suppose that the school reverses its rule in favor of coolness. Where would the gasoline come from? The American wells are at full production. In the past, the oil companies would have imported more from Iran -- but the oil companies are no longer in charge in the Iranian fields. It takes a bit of time to get used to the idea, but the supply is no longer flexible. If the youngsters at Osbourn High go back to driving to school, there will be that much less gasoline for everyone else in Manassas -- and not everyone else has the alternative of free rides in the yellow buses.

By the way, what about those thousands of cars in the student parking lots that surround every other high school in the Washington suburbs?