Prince George's County School Superintendent John A. Murphy appealed last night to state legislators to fund the magnet school plan he implemented this year. He said money problems have become critical because the federal government rejected his application for a $4 million grant this week.

The meeting among Murphy, 15 legislators from the county and the County Board of Education swung between desperate warnings that the school system could close next year and confident assurances that money would be approved.

"If we don't have the money before January, it may be that when the kids go home for Easter break, they may be going home for the year," said board member Sarah Johnson. "We'll have to fold if we don't have the money."

State Sen. Thomas V. Mike Miller Jr. (D-Prince George's) offered a more hopeful reading. "I'm confident the school system is not going to close down in April. The money will be found."

The magnet plan, designed to draw white children into predominantly black schools, was approved for a one-year trial run by U.S. District Judge Frank A. Kaufman, who is presiding over the county's 13-year-old desegregation lawsuit.

The school board is under some pressure to secure funding soon because of an agreement with the county NAACP, the plaintiff in the suit. The agreement, signed and approved by Kaufman this summer, requires the board to take "appropriate legal action" against the state or county if necessary to receive funding.

The magnet plan will cost $8.9 million this year and $12 million in each of the next four years. Although county and state officials have expressed general support for the plan, there has been no commitment of funds.

School officials have already spent $4 million this year on the assumption that the money would be recouped next year from the county or state.

Pleas for some assurance of funding by next year were met with caution by Sheila Tolliver, who represented Maryland Gov. Harry Hughes at the meeting. "There is no way . . . you will know for sure before April . . . the exact posture you're in," she said. The budget process would prevent funding commitments before then, she said.

The news yesterday that the $4 million federal grant application was rejected complicated an already touchy issue. "When you consider it's about half the total we need for this year, it doubles the problem," said school spokesman Brian J. Porter. "Four million dollars is a very difficult sum to generate."

Last night was the first time school officials met formally with the county's delegation to the Maryland General Assembly on the question of funding the magnet schools. Murphy and other school officials left the meeting somewhat bouyed. "There is as a result of tonight a great deal of optimism that the state government and county government will rally behind the school system," Porter said.

The magnet plan includes six schools that offer programs for talented and gifted students and another six that offer before- and after-school day care. The number of magnet schools is set to increase each year for the next several years.

The plan also incorporates 10 predominantly black schools that receive additional funding and staff because school officials say they cannot be desegregated. The plan is the most ambitious to be offered in more than a decade of dealing with the desegregation problem.

Murphy warned the legislators last night that "we are falling rapidly behind every other jurisdiction in the state of Maryland." But he said the money for the magnet schools must not be taken from the county's operating budget, which is already strained, because that "would have a demoralizing effect."