The Prince George's County Board of Education last night unanamously approved a sweeping five-year desegregation proposal that calls for 30 magnet schools, additional funding for 10 predominantly black schools, eight school closings and boundary changes for three schools.

The proposal includes a mandatory back-up busing plan, which would go into effect if the changes do not meet the board's goals for desegregation in the county.

School Superintendent John A. Murphy, who unveiled the plan yesterday, said it will be submitted Monday to U.S. District Court Judge Frank A. Kaufman in Baltimore. He is overseeing the 13-year-old lawsuit brought by the NAACP to force the school system to desegregate.

The $8.2 million plan, parts of which Murphy expects to implement next fall, would be the third major proposal to go before Kaufman in a year. He rejected a school board proposal last spring that would have closed 22 schools and is considering recommendations from a panel headed by Robert L. Green, president of the University of the District of Columbia. School officials believe the Green plan, which would increase busing and close as many as 40 schools, would cost about $65 million.

"Plans have come and plans have gone . . . ," said Murphy. "But now I believe we have found the right answers."

He indicated he would pull back from the plan only if Kaufman issues a conflicting order or if funding is unavailable. County Executive Parris Glendening said yesterday he believes the money will be approved.

The proposal got mixed reviews from two black community groups and was skeptically received by an attorney for the county NAACP, which initiated the desegregation lawsuit.

"What is it about this program that leads the board to think it will be successful?" asked attorney Joseph M. Hassett.

Hassett expressed disappointment with the lag time for the backup busing plan. "We're now 13 years after they were ordered to desegregate and 31 years after Brown [Brown v. Board of Education, the landmark 1954 desegregation case].

"Five years is a long time to wait," he said.

Jeanne Washburn, president of the County Council of PTAs, endorsed the plan. "It seems to encompass so many of the positive goals and ideas that many of the local PTAs have mentioned.

"A lot of the concerns of the parents have been addressed," Washburn said.

Murphy's proposal affects 45 schools now outside, or expected to fall outside, court-established racial guidelines of no more than 80 percent and no less than 10 percent black enrollment.

Under the plan, six magnet schools would be created for the next school year to offer talented and gifted programs for about 700 students. Six more would be workplace schools, which would offer before- and after-school day care for as many as 800 students.

Magnet schools are designed to promote integration by drawing students to special programs from elsewhere in the county. Students would be accepted according to racial guidelines to ensure racial balance at the magnet school.

Murphy also plans to beef up instruction at 10 elementary schools where enrollments are more than 80 percent black. Each of the schools, all of which are close to the District line, would receive two additional teachers, a computer lab, take-home computer program and additional staff training.

Critics said this component of the program is inadequate. "They're letting the all-black schools stay all black and throwing the bone of a couple extra teachers and letting the all-white schools stay all-white," Hassett said.

No schools would be closed in the 1985-86 school year, but two schools would be closed in each of the following four years. Eighteen more magnet schools would be phased in by 1989, offering still unspecified programs.

Glendening said that, after conferring with county representatives in the General Assembly and others, he believes sufficient money will be available from federal, state or county sources.

"There is no agreement on the specifics" of how the program will be funded, he said, "but there is absolute agreement that funding will be available."

Murphy said he hopes to receive as much as $4 million in federal grants earmarked for magnet school programs, and $1 million in revenue from fees charged for day care before and after school. Parents will pay $27.50 a week to enroll a child in these programs.

James Garrett, organizer of the Black Coalition Against Unnecessary Busing, said he prefers the plan over the Green Report. But he expressed reservations that the talented and gifted programs may reinforce racial stereotypes by serving primarily white children.

Alvin Thornton, representing the Ad Hoc Committee on Quality Education, complained that there is not sufficient compensatory funding for the predominantly black schools, and he cautioned that magnet schools have failed in several cities.

Murphy's proposal calls for creation of a 100-member community task force to provide advice on how the magnet school and compensatory programs should be implemented.