Parents in Fairfax County's Mount Vernon District want better-quality textbooks and educational supplies, smaller classes and a revision in the grading system for their school-aged children.

These and other findings were released last week by school board member Gerald Fill, who surveyed PTA leaders in the district he represents on the board.

Fill sent five-question surveys to the 18 PTAs in the district, asking PTA leaders about their major concerns and for suggestions to improve the school system.

Fifteen PTA leaders responded, with the single most common complaint being the need for improved textbooks, instructional materials and supplies. Ironically, the textbook criticisms came only a few days after a controversial proposal by Superintendent Linton Deck that students be charged textbook rental fees. The plan, part of Deck's proposed budget for the 1982 fiscal year, was designed to raise $2.75 million for the schools next year.

Deck's proposal, which already has angered some parents in the county, would appear to be in trouble in the Mount Vernon area, where some parents say they are not satisfied with the condition or availability of the textbooks now being used.

Fill, who has expressed reservations about the proposed rental fees, has called the plan a "slap in the face" to his constituents.

"The school board has to stop being an apologist for the school system," Fill said this week. "We've got to begin being responsive to the taxpayers.

Other findings from the Fill survey include requests for better education and counseling on drug abuse, suggestions for better reading programs, a call for an improved curriculum and a desire for reduced administrative staffing -- another area where the school system has come under fire by school board members and county politicians in recent months.

In addition to specific complaints, Fill said the survey pointed to some overall problems.

"There is a very definite gap between what the school administration think are the student needs," he said, "and the parents' understanding and perceptions of what the students need."