More than 400 people crowded into an Arlington school auditorium last week for a lively discussion over school closings that centered on the county's alternative schools and a plan that would keep all three high school buildings open.

The discussion, part of a series of public meetings the school board scheduled on possible school closings, lasted more than five hours. More than 60 people addressed the board.

The meeting was marked by frequent outbursts of applause as well-organized contingents of parents, teachers and students addressed the pros and cons of the proposals.

This was the last announced public hearing on school closings for a while. Next month the board is expected to make its decision on grade groupings, a preliminary step in the school closing deliberations.

The board has been considering several realignments of grade groupings. At last week's meeting, the plan that brought the most support -- and seemingly equal opposition -- was one known as 6-2-2-2. Under that system, elementary schools (kindergarten through grade six) and intermediate schools (grades seven and eight) would remain. However, the county high schools would be divided into two grade groupings: 9 and 10, and 11 and 12. The high schools currently contain all four grades. The 6-2-2-2 plan would allow the county to use all three high school buildings, with ninth and 10th graders at two buildings and 11th and 12th graders at the third. (The school system also operates a fourth, alternative program, H-B Woodlawn, which includes high school and intermediate grades).

The 6-2-2-2 plan won its strongest support last week from teachers and parents of students at Washington-Lee High School. Teacher Candy Frankel told the board that the faculty had voted unanimously for the plan.

"It would keep all three buildings open, unifying the county rather than dividing it," she said. "It would improve community cohesiveness rather than polarizing it. . . . Ethnic diversity would be automatic, there would be equal opportunity for special programs and advanced placement classes and it would broaden the selection of course offerings. It would increase competitive athletics . . . and it offers the greatest flexibility."

Other supporters said the plan would improve school spirit, provide more opportunities for leadership and sports participation (because lowerclassmen would not be competing with juniors and seniors), permit increased teacher attention to freshmen and sophomores and give greater flexibility for dealing with enrollment changes.

But the plan had detractors who were as vocal as the supporters. Anne Alexion, a Yorktown teacher, said she was "appalled" by the proposal.

"You would lose academic continuity by moving the students every two years," she said.

Alexion added that course selections could actually be fewer as lowerclassmen lose the opportunity to take classes normally offered only in upper grades.

"Can we really offer all these different courses at each school?" she asked, citing the duplication and extra costs that would be involved.

The 6-2-2-2 plan also opened a debate over the county's three alternative schools. Although all three have become increasingly popular, as evidenced by the long waiting lists at each, they also have been the focus of a continuing community debate. In addition to H-B Woodlawn, the schools are Drew Model and Page Traditional, each with differing educational philosophies.

For the most part, supporters of the 6-2-2-2 plan came down against the alternative schools, and said they saw the plan as a way of eliminating them.

Calling the alternative schools "elitist," parent Michael McMorrow said the special schools should be closed because "they are damaging the regular schools by taking out a very special group of children. . . . Their existence has divided the community at a time enrollments are going down and costs are going up and the divisiveness is becoming a real problem."

"They are a luxury we can no longer afford," added Clay Woods, past president of the Barcroft Elementary PTA. "We should apply the lessons learned [from the alternative schools] to the neighborhood schools."

But the alternative schools also had a large contingent of supporters.

"There are some kids who just don't fit into the regular programs and these schools are needed for them," said Thomas Rippey, a parent.

Other speakers countered the argument that the alternative schools are elitist.

"The question should not be whether Page is the best in the county, but a question of best for whom?" said Page parent Karen Rosenbaum. "Page and Drew need to exist for all of us."

Rosenbaum reluctantly suggested eliminating kindergarten classes at Page, thus forcing parents to send their children to kindergarten at neighborhood schools. Such a change, Rosenbaum said, would allow parents to become more familiar with neighborhood schools and might convince many that Page was not the only school appropriate for their children.

As in other school systems, Arlington has faced serious enrollment declines over the last decade, and school closing proposals have become a regular item of consideration. Any closings approved by the school board would go into effect in fall 1984.

Before final plans are announced, however, the board expects to schedule several more rounds of public hearings.