THE CONTRAST between school enrollment policies in Montgomery and Prince George's counties is striking--and not to Montgomery's advantage. The question in both school systems is one of the most difficult in local politics: how does a predominantly white suburb accommodate the children of an increasing black minority without segregation, and yet without busing kids unacceptably long distances?

On Monday, after hearing eight weeks of testimony on race and schools in Prince George's, Judge Frank A. Kaufman commented: "It seems to me that those who have been running the school system have been running it in good faith." The country's NAACP has been pressing the argument in this case that the county never fully desegregated its schools, and never did enough to maintain racial balance. But it's clear that the school system did a remarkable job in a period of rapidly rising numbers of black children in its classrooms, and declining numbers of white children.

On Wednesday, the Maryland Board of Education ruled that the Montgomery school board had erred in dealing with three schools that have relatively high ratios of black students. These three have been important prototypes in the county's evolving racial policies; for example, Rosemary Hills Elementary School has been paired with a school in Chevy Chase. But the board voted last fall to close Rosemary Hills and disperse the children widely among other schools. Marian Greenblatt, a member of the Montgomery school board, argues, correctly, that closing Rosemary Hills would result in greater desegregation--at least in the arithmetical sense of more uniform racial ratios. But black parents have bitterly protested the unfairness of a policy that buses their children whatever distances necessary to keep those ratios down.

The solution applied by Mrs. Greenblatt and the Montgomery school board at Rosemary Hills bears a striking similarity to the solution that the NAACP has been seeking in Prince George's. They are both wrong. Busing is a valuable method of avoiding disparities in small systems, or among neighboring schools. But there comes a point at which the many costs of long trips for the children outweigh any educational advantage. A school board has an obligation to go to any reasonable lengths to avoid imbalances, but beyond that its job is to educate the children where they are.

The eight weeks of testimony has confirmed the impression that Prince Goerge's has been meeting its responsibilities intelligently and honestly. Montgomery County--despite its greater resources and more stable population--has made serious mistakes that the state has now, justifiably, reversed.