THE COURT'S latest decision in the Prince George's County school desegregation case represents both good law and good sense. Frank A. Kaufman, the federal judge presiding over this long suit, has now told the county's school board to proceed with its plan for magnet schools. He wants the school board to develop the magnet schools faster than it had originally proposed, and he suggests that the plan may eventually have to be supplemented by more busing. But Judge Kaufman has declined, at least for the present, to rely on the great expansion of busing that his advisory panel had unwisely recommended.

The great virtue of the magnet schools is that they will attempt to achieve a more satisfactory degree of racial desegregation by purely voluntary reassignments. Parents will be offered incentives to move their children to schools that provide programs not available at their present schools. In some cases it will be special instruction for unusually bright children. In others it will be day care before and after normal school hours. To the extent that parents can be persuaded to move their children voluntarily in directions that also serve the larger public purpose, this strategy deserves to be tried first.

Busing children can be a useful way to advance desegregation: and it has been used extensively in Prince George's. But circumstances there do not favor unlimited reliance on it. The county is too big. The distances are great and the bus trips become excessive. There's an interesting comparison between the Prince George's and Alexandria school systems -- the two that, in this metropolitan area, deal with the most diverse populations. Alexandria has for years relied on buses and school pairing to maintain desegregated classrooms in the lower grades. For the upper three grades, all questions of racial and social balance are resolved by having only one senior high school in the city -- one which, incidentally, has won national recognition for its success in serving a very wide range of students. Scale makes a difference. Solutions that work well in a small city will not suffice in a school district such as Prince George's, which, both in enrollment and geographical size, is one of the country's largest.

The Prince George's school suit is now in its 14th year. The reason for this long and extremely expensive litigation is that in the past the school board has repeatedly followed mistaken interpretations of the law and wasted much time and money on appeals in which its chances of winning were poor. But in recent years the board's attitude and purpose have changed. It is is now moving with imagination and skill to meet its responsibilities. Judge Kaufman, recognizing this change, is responding by allowing the board increased discretion to design its own remedies. This kind of cooperation can only benefit the children who go to school in Prince George's.