Sally Bealafeld's kindergarten classroom is overflowing with children.

There are children at a table reading aloud from a book about shapes.

There are children chattering at another table as they cut out Pilgrim hats for a Thanksgiving party.

There are children on the floor assembling number toys.

There are so many children in kindergarten at Canterbury Woods Elementary School in Annandale, where Bealafeld teaches, that a blue pegboard reserved for every child's name card is not big enough. Five tags are attached to the adjoining cinder block.

Last year, the Fairfax County school had 37 kindergartners. This year, there are 54 of the baby boomlet's 4-, 5- and 6-year-olds -- 29 in the morning class, 25 in the afternoon.

Principal Shirley E. Bealor would love to see smaller kindergarten classes.

When it comes to giving personal attention, "Every additional child makes a difference," she said.

Just as increased numbers of kindergartners are hitting the schools this year, county officials are feeling pressure from parent teacher associations and School Board members to reduce the number of children in each kindergarten class.

Fairfax County, with an average kindergarten class of 23.8 children, has more than the average class statewide, 21.8. Nearly half the county classes last year had 25 or more children, and this year's figures, to be released officially in the spring, are likely to show little change.

Supporters of smaller classes argue that children need a lot of personal attention in their first year of public school.

But others point out that every kindergarten class has a teacher's aide, that school facilities are strained already without adding extra classes, and that other priorities may come first.

Reducing class size may seem a luxury in poorer school districts, but it commands attention in Virginia's richest county, where parents expect first-class education.

"To pay the taxes that are here -- I don't mind paying them, but I expect a quality school system," said Diane U. Waller, who has a son in a kindergarten class of 29 at Haycock Elementary School in Falls Church.

"I'm so disappointed for my initial exposure to be a classroom stuffed with children."

The kindergarten parent lobby is growing fast. Fairfax County's kindergarten population grew by 500 between September 1984 and September 1985, when it reached 7,984.

Fueled by new housing and a baby boomlet, it is predicted to reach more than 9,800 by 1990.

"This is just the beginning of it," said Waller, who expects to send her 2-year-old to Fairfax County kindergarten in three years.

"The problem is only going to get worse."

Haycock's PTA has written to the county School Board and superintendent asking that no kindergarten class be larger than 24 pupils. State law and county guidelines set a maximum of 30.

Kevin Bell, president of the Fairfax County Council of PTAs, said other PTAs have raised the issue and that his group probably will consider recommending a lower kindergarten maximum at its next meeting.

"It seems to be a broad-based concern across the county," he said.

School Board members Katherine Hanley and Olivia Michener asked the superintendent's office to report on what it would cost to lower kindergarten class size.

In the first through third grades, the county requires a 24:1 ratio of pupils to teachers.

In schools with "special needs" -- mainly those in low-income areas, with high pupil turnover or large numbers of foreign-born pupils -- that ratio is 22:1.

Courtney Pelley, the principal at Haycock, said she favors a maximum of 24.

"No matter how wonderful a teacher and an aide are, they can't give children as much attention" in larger classes, Pelley added.

The county's teacher associations -- the Fairfax Education Association and the Fairfax County Federation of Teachers -- favor smaller kindergarten classes, and the FEA has urged a maximum of 24 in classes at all grade levels. But the groups say they are no less concerned about class size in higher grades.

And the push for smaller classes does not have unanimous support on the county School Board. Chairman Mary E. Collier said kindergarten is "among many areas where we need to look at reducing class size," but she pointed out that the presence of an aide takes pressure off the teacher.

Joy G. Korologos, the board vice chairman, said a lack of classroom space stands in the way of smaller classes.

And, she said, "If we had our druthers, I think all of our class sizes would be lower. But we have to weigh priorities in the budget."