A court-ordered plan under which some 16,700 students are now bused for racial balance, was voided today by the same federal court that ordered it.

The action leaves the school board, a majority of which opposes busing, free to do what it wants with respect to desegregation, said school board co-counsel Leo Krebbs.

The court decision is significant because it involves a complete reversal in which the schools here were first told, in effect, that full-scale desegregation was necessary, and then were told it was not.

The district, in which many residents were opposed to busing, had gone along peacefully when full-scale busing began Sept. 2, 1976, after more than four years of legal battles.

However, the U.S. Supreme Court, ruling in June on an appeal by the Dayton school board, concluded that the evidence in the case did not justify the system-wide desegregation plan imposed by U.S. District Court Judge Carl B. Rubin. The high court sent the case back to Rubin for new hearings on the matter, which were held earlier this fall.

Under the plan thrown out today, each school in the 38,000-student district had to come within 15 percentage points either way of the district's actual racial radio at the time the plan was imposed. At that time it was about 48 per cent black: Today it is over 50 per cent black.

In his new order yesterday Rubin said it had been up to the plaintiffs (led by the NAACP) to prove that there was a deliberate intent to segregate and that there was "an incremental segregative effect." This was needed, said Rubin, to show a violation of the equal protection provision of the Fourteenth Amendment. Rubin said they failed to do that and dismissed the case.

The decision apparently leaves the district free to drop the busing plan at the beginning of the second semester, and though school administrators were not immediately available for comment today, the district is expected to do so. Some officials had said that this busing was expensive, and a factor in the school district's pressing financial situation as well as in two sound defeats by Dayton voters of needed tax increases.

The NAACP said it would appeal.

NAACP assistant counsel Richard Austin said here that the decision was a bad precedent and that if other cases resulted in similar rulings elsewhere, "we would be back to pre-Brown vs. Board of Education days in which we hadsegregated schools."