IN ITS QUIET way, Alexandria's school system has become a model of enlightened racial policy. Serving an extremely diverse population, it is in many respects the Washington area's most successful example of school desegregation. Unfortunately, the Senate has recently passed a bill on court orders and busing that, indirectly but effectively, jeopardizes Alexandria's progress. The city's school superintendent, Robert W. Peebles, discusses that danger in a letter appearing on this page today.

None of Alexandria's schools is noticeably whiter, or blacker, than the others. That reqires some busing. It's voluntary, and owes much to strong community leadership. There has never been a court order to require it in Alexandria. But you would have to say that the possibility of a suit was much in people's minds at the time of the crucial decisions. When Alexandrians disagreed about other things, they were at least able to agree on the desirability of avoiding litigation. The process of constitutional compliance worked well.

The bill that the Senate passed would forbid federal court orders that require busing beyond very narrow limits. In the literal sense it doesn't apply to Alexandria, since Alexandria stayed out of court. But in reality, obviously, it would remove any sanction against retrogression. That would constitute an invitation to reopen old questions and old quarrels long since closed. And that is what Mr. Peebles is worried about--with justification.

He is offering a useful warning that the impact of the Senate bill will be much wider than a first glance might suggest. It will have an effect in any school system where there are strong racial patterns in residence. Alexandria is a small city, as cities go, but it couldn't maintain its present racial balances, school by school, under the Senate's restrictions.

Alexandria is running a first-rate school system. The bright kids go to good colleges. Students not interested in college have access to a sophisticated and efficient program of vocational education. For 11,000 children, it is as good a working demonstration of equal opportunity as you are likely to find. The Senate bill is an attack on it.

The House has passed a much less damaging provision, on which the Senate refuses to act. The Senate's bill has arrived in the House but, again, there's been no action on it. The public interest would be best served if neither of them moves an inch.