AT ALEXANDRIA'S T.C. Williams High School, students complain that the shortage of parking spaces violates their constitutional right to drive to school. The other day they demonstrated in support of the right to park with a bit of marching and sign-waving. It's always deeply gratifying to see young people take seriously the fundamental issues of civil rights.

One response to the students' grievance is to expand the school's parking lots-- presumably into the adjoining park. Another is to tell the youngsters to take the bus.

There is no high school in all of the Washington suburbs will less reason to encourage students to drive to school. T. C. Williams High serves a compact city with excellent bus service provided by both the school system and Metro. One student objected that the Metro bus is too expensive. As an exercise in Arithmetic for Everyday Life, she might try calculating the cost to her of driving. Then she might estimate the the cost -- to the city's taxpayers, this time -- of each parking space.

A small number of the school's students really do need cars to get to jobs that they hold under T. C. Williams High's valuable and successful work-study programs. They deserve priority for parking spaces, which means excluding all the cars of students who really don't need them. As for the constitutional question, litigation does not seem advisable. The courts have been reluctant to accept the view that freedom of expression includes driving to school.

The squeeze in the parking lots has been created by a reorganization that increased the school's enrollment. But it's not just a matter of finding more space for parking -- although in an urban neighborhood that's not simple. The waste of gasoline is the main thing. The country's supply of gasoline is now running just about 300 million gallons a day. That sounds like a lot but, in fact, it's just about the same amount available last June when the gasoline lines were at their longest.

Gasoline supplies have not increased significantly over the summer. The federal allocation rules are working more smoothly, and the surge of hoarding and tank-filling has ended. But, much more important, a lot of Americans have cooperated in driving less. If they return to last year's patterns, the lines will reappear. High school students could make a useful contribution by exercising their right to leave their cars at home.