The Magnet School plan is off to a successful start in Prince George's County. The school system has put much energy and imagination into the magnet schools, and parents have responded enthusiastically. The purpose is to draw white children into schools where the enrollments would otherwise be almost entirely black. As a way to increase racial desegregation of schools, it is particularly attractive because it depends on voluntary acceptance of real incentives. But this strong beginning ought not distract attention from a decision that is probably not very far ahead of the county. At some point the county and the courts will have to decide whether desegregation needs to remain the primary consideration in the organization of the school system or whether changing circumstances are not making it secondary.

That decision will not be up to the county school board alone. The Prince George's chapter of the National Association for the Advancement of Colored People, the principal plaintiff in the litigation that has been proceeding since 1972, will have an important part in it. Parents and civic organizations certainly have an interest in it. Any change in policy would have to be ratified by the courts.

It is doubtful that the Prince George's schools will ever meet the standards of desegregation that the courts have set. Many of the county's schools were racially identifiable, as the judges put it, in 1972, and many of them remain racially identifiable today. What circumstances could justify setting aside the pursuit of pristine desegregation in favor of other educational goals?

First, there has been a profound change in the attitudes of the school board and administration. After inordinate foot-dragging earlier, they have swung around and in recent years worked in genuine good faith to serve all children equally. That's a crucial difference. Second, there is the ineluctable fact of a changing population. Black children now outnumber white children in the county's schools by nearly two to one. In a small and compact school system, busing is always a useful solution -- as in Alexandria, for example, where one senior high school serves the whole city. In sprawling Prince George's, physical distances often make busing onerous, particularly for small children.

And there is a certain dilemma in the magnet concept. To attract children it must promise unusual resources, and to attract white children it must reserve those resources specifically for them. Some of the magnets in Prince George's provide extended day care. Many black children have now been put on waiting lists for this program while space is held open for white children. That's defensible up to a point, but it's also a warning that the magnet plan can't be expanded indefinitely without creating new inequalities of its own. Prince George's is now approaching a stage at which it will have to look beyond racial head counts to other and possibly more significant measures of equal educational opportunity.