Prince George's County school officials, responding to recent criticism that the county's magnet school desegregation plan is unfair to black students, released statistics yesterday that they say demonstrate that blacks are reaping most of the benefits of the program implemented last fall.

"There is certainly a misconception that white students are benefiting more than blacks," said School Superintendent John A. Murphy. However, he said, "There is more money and programs going to black students than white students."

Murphy released figures showing that black youngsters make up 39 percent of the enrollment this year in six magnet programs for talented and gifted students. That is just short of the goal of 40 percent for black enrollment that was set when the program was designed last year.

The figures showed that per-pupil expenditures are significantly higher in programs for talented and gifted students than in 10 predominantly black "compensatory" schools that officials say cannot be desegregated. But officials contend that because expenditures will rise substantially in the compensatory schools and drop by a similar percentage in the programs for talented and gifted students now offered at six magnet schools, black students will be getting the lion's share of funding in the desegregation effort.

Officials also said that an array of new magnet programs proposed for next year will enroll more black students than the programs for talented and gifted students, which require students to pass an entrance exam and are only available to selected students. Most of the new magnet programs will be housed at predominantly black schools and will offer special programs, such as a back-to-basics curriculum, for all students at the schools.

Critics of the program, however, said they were not satisfied by the new information. Richard (Steve) Brown, executive secretary of the county NAACP, said, "We can't be persuaded by projections." And, he said, spending comparisons for compensatory programs and those for talented and gifted students "simply verify that too much is being spent on a few white youngsters."

The Prince George's County Council last week raised similar criticism and urged the Board of Education to delay its vote, scheduled for tomorrow, on a proposed expansion of the magnet plan.

"My opposition remains," said County Council member Hilda Pemberton, "until we have an idea how our money was spent last year . . . if in fact it was spent well and if it made a difference."

Last month, Murphy proposed adding 20 magnet programs to the present 12 by the 1987-88 school year.

The figures released yesterday also indicated that:

*In the 16 new magnet programs proposed for next school year, black enrollment is expected to exceed 50 percent.

*Black students make up 80 percent of the enrollment in the magnet schools that offer before- and after-school day care this year.

*Per-pupil costs for students in the predominantly white classrooms for talented and gifted students this year were $736 above the countywide base of $3,370, but included the one-time costs of special equipment such as computers. Next year the cost per pupil will be $347 above the county base. The per-pupil cost in the predominantly black compensatory schools this year was $396 above the base, but will rise to $623 when all-day kindergarten is added and new teachers are hired to reduce class size.

*Of 2,830 additional students who will be bused under the expanded magnet plan, nearly 68 percent will be black. School officials say this is in line with countywide enrollment, projected to be 61 percent black next school year.