A coalition of parent groups in Prince George's County blasted the school superintendent's proposed 1981 budget yesterday, claiming the belt-tightening measures would push the county's school system "on a toboggan slide to mediocrity."

For the first time in seven years, the budget committee of the 20,000-strong County Council of Parent-Teacher Associations instead recommended a higher budget, including $4 million to restore 240 teacher positions that were trimmed this year.

In their 10-page report, presented to the council of PTA's yesterday, the budget committee recommended against adopting superintendent Edward Feeney's proposed $287.6 million budget, which would slash 625 positions from the school system's personnel rolls. Feeney would also cut support for high school interscholastic athletics by 50 percent.

Instead, the committee recommended asking for $290.8 million called for the closing of 21 schools, 15 elementary and six junior high.

The council also recommended that $2 million be added to the budget for 22 elementary art positions, an expansion of the talented and gifted (TAG) program. They also asked that the junior high school interscholastic program be restored.

"If we're talking about educating every child," said PTA council president Joanne Brown, "art, music and athletics are just as important and basic as the 3 rs. This is the first time we've come out against the superintendent's budget in its entirely. A lot of people feel it just isn't emotionally sound."

The school closings were urged to counterbalance the additions to the superintendent's budget. Under the committee's plan, the school board could expect to save $2.6 million the first year and add $3 million in future years by closing all elementary schools with fewer than 300 students and all junior high schools with fewer than 600 pupils.

"Many of the smaller schools are already being shortchanged," Brown said. "If we close these schools, the students would be able to take advantage of the increased teaching and other resources in the larger schools." a

School board chairman JoAnn T. Bell said yesterday that it was doubtful that any of the closing would occur this year. She did say, however, that Feeney's budget was too austere and that quality education might eventually be the victim.

"I don't see how we're going to be able to keep asking the people who run our school system to absorb these budget cuts and give twice as much in the way of effort," she said. "We've started to inflict wounds in our educational system which may bleed it to death."