Prince George's County Executive Parris Glendening proposed a fiscal 1987 education budget of at least $363.3 million yesterday, which school officials promptly denounced as a "woefully inadequate" amount that will "limit rather than improve" the county's desegregation efforts.

Glendening's proposal touched off what he predicted will be a "difficult" budget season as Prince George's seeks ways to finance its new magnet school program in spite of a substantial loss of federal revenue sharing and a generally tight fiscal picture.

The school budget, which includes both capital and operating outlays, could go as high as $380.7 million, Glendening said. That figure would include about $17 million the county hopes to get from the state to fund the second year of its magnet plan, implemented this year to improve racial balance in the schools.

But if state legislators do not come up with funding, Glendening warned that educators will have to dip into their operating budget to fund the second year of a new magnet school program.

Glendening's announcement was the first round of what has become an annual budget battle between the executive and Board of Education members, who will approve their own budget recommendations this spring. A final budget must be approved by the County Council before June 1.

The fight for funding has become almost a given in the county since a property tax limitation was approved several years ago.

"I think we're going to be in dire straits if that's all we get," Board of Education Chairman Angelo Castelli said after meeting with Glendening.

The board said in a prepared statement that even the most optimistic revenue picture presented by Glendening "failed to address the most pressing needs of the school system," including its average class size, which is the largest in the state; its funding for instructional materials, which is the lowest in the state; and its teacher salaries, among the lowest in the Washington area.

Yesterday, in the wake of Glendening's proposal, the board called for new revenue sources, including taxes, to provide additional funds for the school system.

"We have the momentum for improvement in our school system now, and we must not lose that momentum," the board said in its statement.

The momentum is widely seen as embodied in the magnet plan that officials hope will resolve a long-standing desegregation court order. The plan, slated to be phased in over the next four years, eventually will include 26 magnet schools designed to draw white students to special programs at predominantly black schools. It also funnels additional funds to 10 predominantly black schools that officials say cannot be desegregated because of their locations.

Glendening's proposed budget, which accounts for a 5 percent wage increase for school employes, also drew fire from the county teachers union. Negotiations on a new teachers' contract are to begin in about three weeks.

"I don't think the teachers will accept it," said Paul Pinsky, president of the Prince George's County Educators Association. "I don't think county officials are going to be able to attract the teachers or retain the teachers they have with a 5 percent settlement," he said.

Glendening said county funds will not cover a wage settlement exceeding that figure and school officials would be forced to absorb any additional cost by making cuts elsewhere.

"The figures are very tight, there's no question about it," said Glendening.

In a letter to Castelli, Glendening cautioned that "the upcoming budget process will be a difficult one" because the county has lost $11 million in federal revenue sharing, which has historically gone to education.

"I would not tolerate any reduction" in services, he said in a telephone interview, adding that the county and school system will be forced to absorb the costs to fund the magnet plan if necessary.

State Sen. Thomas V. (Mike) Miller said the county delegation to the state legislature is committed to funding the magnet plan, but will face a bleak financial climate during the 1986 session because of the recent savings and loan crisis.

"It's going to be very difficult" to secure magnet funding, he said, "because it's unique to Prince George's County."