The Justice Department asked the Supreme Court yesterday to uphold a school desegregation busing plan in Dayton, Ohio, that Dayton officials claim is too severe.

At issue is a U.S. District Court order, which was upheld by the Sixth U.S. Circuit Court of Appeals in May. It calls for implementing a plan that would require busing about 15,000 students and require 66 schools in the system to have a black enrollment of between 33 and 63 per cent.

In a friend-of-the-court brief filed last night, the Justice Department told the Supreme Court, which is reviewing the case, that it disagrees with the reasoning applied by the appellate court in upholding the order.

However, the department's brief added, there is massive evidence in the case to show that Dayton officials had engaged in systematic efforts over the years to maintain racially segregated schools.

The brief cited the principle stated in past Supreme Court decisions that where officially created segregation is shown to exist it must be rooted out completely. It also argued that if discrimination is found in a few schools, the courts are entitled to assume that the practice is widespread and put the burden on school officials to demonstrate otherwise.

Therefore, the department's brief said, the desegregation plan does not appear excessive in light of the evidence, and it called on the Supreme Court to uphold the lower court decision "since it is the judgement of the court of appeals, not its reasoning, that is at issue here . . ."