U.S. District Court Judge Frank A. Kaufman today dismissed what he called an "11th hour" motion by lawyers for the Prince George's County school board to disqualify himself from hearing further testimony in the desegregation suit brought against the county schools by the NAACP.

Lawyers for the school board charged in a motion filed today that Kaufman should be disqualified because of a disagreement between him and the schools over the scope of his sweeping 1972 desegregation order, which the NAACP contends was never fully implemented.

Kaufman insisted that the disagreement -- over whether guidelines he issued 10 years ago for the percentage of black students in individual schools should have increased as black enrollment incresaed -- is not grounds for removing himself.

The issue was sparked last week when Kaufman said that it was his tentative understanding of the law and his own rulings that the county had a continuing affirmative duty to maintain racial balance in its schools even after he relinquished control in 1975.

School board lawyer Paul M. Nussbaum immediately argued that he did not understand Kaufman's original desegregation order or the subsequent release of the schools from his custody to mean they had such an affirmative duty.

The issue arose as Kaufman examined evidence last week about what happened to black percentages at individual schools after he ordered that every school should be between 10 percent and 50 percent black.

Kaufman conceded that there was no mention of a sliding scale in his guidelines, but another attorney for the school system, Alfred Scanlon, said the fact that Kaufman acknowledged that he had the guidelines in his mind was grounds for complaint.

"We reject totally and affirmatively the concept that we were under the obligation to maintain any guidelines," said Scanlon, adding, "We are not just pulling this out of thin air."

Scanlon later complained that the board and its lawyers were shocked at finding out about the idea of continuing guidelines last week, and called it unconscionable.

"It wouldn't be the first time that defendants were shocked that the law was not what they thought it was," Kaufman replied before rejecting the motion.

The disagreement took up all of the time on this start of the third week of the civil action in U.S. court here.