The Prince George's County NAACP said yesterday statistics show the county is operating a segregated school system in violation of a 1972 federal court order. The NAACP pledged to reopen a desegregation suit unless steps are taken to meet the court's racial guidelines.

Citing a 23-month study of the county schools financed by the national NAACP, spokesman John Rosser said there are almost as many substantially one-race schools in the county today as there were before the court order was implemented early in 1973 through a controversial busing plan. Rosser said the NAACP will go back to court unless the county school board moves to comply with the federal court's guidelines of no less than 10 percent or greater than 50 percent minority enrollment in any of the county schools.

School board members and school officials said they had not yet studied the NAACP's arguments but blamed any increase in substantially one-race schools on the shift in population over the last decade during which the percentage of black students went from 21.3 percent in 1972 to 49.9 percent last fall.

Among the steps that national NAACP General Counsel Thomas I. Atkins asked the board to consider is alteration of its plan to close 43 schools beginning next year.

Rosser, former chairman of the county NAACP education committee, said that despite school board projections, past school closings and other decisions have resulted in increased segregation in the schools.

At a press conference, Rosser and the new education committee chairman, Archie L. Buffkins, stressed that they were not focusing on more school busing as a remedy for the steady increase in "racially identifiable schools." They said that specific ideas to increase integration would have to be worked out with the school system.

Paul Nussbauum, the board's attorney, said the school system is still in compliance with the order to "dismantle the last vestiges of a dual school system. . . . When the court closed its file on the case in 1975, it was without any opposition from the plaintiff. I must take the position that the system has effectively desegregated and the system has done nothing to resegregate since them . . . ."

Buffkins said statistics, including those showing a disproportionate number of black suspensions and underrepresentation in programs for gifted students, indicate a problem beyond the legal requirements.