The Prince George's County Board of Education yesterday announced an agreement with the county NAACP, its longtime opponent in a desegregation lawsuit, on the specifics of a plan to integrate the county school system.

The two sides, engaged in often acrimonious litigation since 1972, moved closer to resolution last month by agreeing to the concept of a magnet school desegregation plan that later won preliminary approval from a federal judge. But the "memo of understanding" filed yesterday in U.S. District Court in Baltimore, represents the first time in years that they have agreed on the nuts and bolts of a desegregation plan.

"I think we're entering into an era of cooperation," said School Superintendent John A. Murphy. " . . . We'll be getting away from this confrontation."

The agreement resolves many of the complaints the NAACP had with the magnet school plan. For example, it requires the school board to seek significantly more funding for 10 predominantly black schools that the board argues cannot be fully integrated. It includes the stipulation that the board must sue the state if it cannot otherwise obtain sufficient funds. Murphy said the decision on whether such a suit would be necessary would be made within a few weeks.

The agreement also limits the board to establishing only six talented and gifted magnet schools, which the black community believes may benefit white children more than black children.

The school board got its way, however, in securing three years to test whether its magnet plan can sufficiently integrate the system of 175,000 students. But the agreement requires the board to be ready with a specific backup busing plan that would go into effect in 1988-89 if the magnet plan fails.

The agreement is the most recent in a series of actions in which the board and the NAACP have waivered over the desegregation issue. It comes only a week after the board appeared close to appealing a 1983 desegregation order to the Supreme Court, a move widely condemned by the NAACP and the community. Wednesday, the board voted 7 to 2 not to appeal after three board members switched their votes in response to the community outcry.

The two sides, however, have been in agreement for about a month on giving the magnet plan a chance. The plan is designed to improve integration by drawing students out of their segregated neighborhoods.

Both sides yesterday expressed satisfaction with their agreement, reached at the direction of U.S. District Judge Frank A. Kaufman after a week of intense negotiation.

"I think the agreement provides a good framework in which to begin implementing the magnet school and compensatory education plan," said William Bradford, attorney for the NAACP and other plaintiffs.

Board Chairman Angelo Castelli said the agreement indicates "everything is on track for next year." He added: "I think it's the first time the NAACP decided to sit down and negotiate."

Among the provisions in the agreement:

*No more than the six talented and gifted magnet schools already planned to open this fall will be established in the future. But eventually those six schools will be made up entirely of talented and gifted students, and regular students will be sent elsewhere.

*The school board agreed to study and eventually reduce the number of black students who are being unnecessarily bused or bused long distances.

*The board agreed to hire and promote qualified black employes throughout the school system.

*In the 10 predominantly black schools, the board must seek sufficient funding to provide all-day kindergarten, class sizes of 20 students, before and after school tutoring and summer school remediation.

*A backup busing plan, if necessary, would bus students no longer than 35 minutes and affect only schools with less than 35 percent or more than 80 percent black enrollment.