A proposed residential high school for Maryland's brightest mathematics and science students is a good idea whose time hasn't come, the president of the State Teachers Association said yesterday.

"In principle, we favor the idea," said Beverly L. Corelle. "But we question the wisdom and the equity of lavishing so much of the state's educational resources and attention on 600 of the brightest and most gifted high school students in the state at a time when so many of our poorer school systems are starved for funds."

Gov. William Donald Schaefer, who proposed the school in line with his economic development philosophy, has included $10 million in capital costs and $3.5 million in start-up costs for the school in his fiscal 1988-89 budget.

Corelle said there are higher educational priorities. "We need to address first the overcrowded classrooms, the short supply of textbooks and other materials, the rising dropout rate in our schools and the underachievement of so many of our students," she argued.

Corelle added that higher pay for teachers also is badly needed. And she said she is concerned that teachers in the school would be exempt from state certification rules, and that students would not have to meet the state's regular graduation requirements.

"What we're saying is the math-science high school is sort of like icing on the cake, and we don't have a cake yet. We're just mixing the batter."

Similar concerns were voiced by legislators at a hearing in the Senate Economic and Environmental Affairs committee earlier in the week.