For students at Osbourn High School in Manassas, life in the fast lane came to a screeching halt this week.

Invoking the cause of energy conservation, school principal Victor Egidi, acting on a school board recommendation, has ordered the school's 899 students to make what some feel is the ultimate sacrifice -- stop driving their cars to school.

Although the ban -- the first of its kind in the Washington area -- is only two days old, it appears to be working. Yesterday there were only 46 student cars at the school, one-third the number school officials said could have been found there last year. Each of these cars had a required special permit for students unable to use school buses.

Most students are accepting the ban with surprisingly little grumbling, though some argue that part of their American birthright somehow has been tampered with.

"A lot of people were disappointed," says Kathi Brusso, a senior. "There's a real feeling here that it's cool to drive to school and people don't want to give that up."

"I was upset," says junior Ellen Anastasi, whose request for an exemption so she could drive directly to an after-school job was rejected. "I can see their [the school administration's] point, but it's such a small school that I can't see how this will save much gas."

Egidi concedes that the driving ban, while a large step for Osbourn's students, is a small step when it comes to the nation's gasoline savings. But he said the energy crisis has given educators an opportunity to teach some important civics lessons to their students.

"There are situations that call for sacrifice on the part of the individual to help the whole," says Egidi, who has been Osbourn's principal since the school opened two years ago.

"The kids have to think about what we're leaving for the next generation. What kind of legacy is a dry [oil] well?"

So far, none of the larger public school systems in the metropolitan area has followed Manassas' example, though a number have other plans to cut back energy use. Montgomery County deputy school superintendent Harry Pitt recently asked principals to work with parents and student groups to devise ways of discouraging students from driving to school. But Lib Boone, his assistant, says, "We certainly haven't ordered any specific restrictions."

Fairfax County schools claim to have saved $150,000 this summer by turning off air conditioners, but restricting student driving, a spokesman said, is "a local school option and we don't know of any that have done it."

The only other nearby school system to curtail student driving is Northumberland County in Virginia, located on the banks of the Potomac where it empties into Chesapeake Bay. Superintendent Kenneth Walker said that only working students among the 350 high school students there can drive cars to school this year. Last year about 280 students drove to school.

The driving ban in Manassas is part of a nine-point program approved by the city's school board in response to pleas from President Carter and Virginia Gov. John N. Dalton for energy conservation. Under the plan thermostats are raised in summer and lowered in winter, field trips cut by one-third, and double and triple-header sports events the rule, not the exception.

The driving ban is by far the most painful part of the plan for Manassas students. To ease the transition the school is providing a special bus to take home students involved in after-school activities. Also, seniors with abbreviated schedules and those in a special work-study program who must leave school early for their jobs are granted exemptions. Those with medical appointments can get a one-day parking permit.

"It will be inconvenient for a while, but once they get used to riding the activities bus, we think they'll like it," says assistant principal L. A. Rorrer.

But the biggest inconvenience may be not for students, but for parents who'd rather lend their children a car for the day than pick them up after school or have them wait for the bus.

"I'm soaking wet," said Barbara Geris, who braved yesterday afternoon's rainstorm to pick up her son after football practice. "I don't believe the school has the right to tell us we can't let our children drive."

School officials say Geris' sentiments so far are in the minority. But they concede opposition could grow.

"I'm afraid the first time we have to tow a car from the parking lot, we'll really see how people feel," says Egidi.