When the Fairfax County school superintendent's office sent word that enrollment declines in the McLean area would require some classroom closings by 1982, angry parents mobilized for action.

But the result of their meetings was not a resistance campaign. Instead, the mothers and fathers, after studying the situation for themselves, recommended the School Board close Pimmit Hills Elementary School near Tysons Corner in Falls Church and Lewinsville Elementary School in McLean. The board agreed.

County Supervisor Nancy Falck (R-Dranesville) says much credit for calming what could have been a nasty dispute goes to Mary E. Collier, the School Board member she appointed in 1979.

"She doesn't wait until the yelling starts," Falck said. "She can see when something's coming along, and work with people."

That observation is echoed by others who have worked with Collier, 43, a civic activist and former PTA president who has been board chairman since 1983. These days, her talent for negotiation and compromise faces what some see as its toughest test, as the board grapples with its proposed 1987 budget and with a perception by some observers that political pressure on the board is increasing.

Collier entered school politics a decade ago, when she and other Dranesville parents, disturbed by cuts in the education budget imposed by the Board of Supervisors, encouraged Falck, then a School Board member, in her successful campaign for supervisor. Collier, a two-term president of the Chesterbrook Elementary School PTA, was Falck's campaign manager.

Collier grew up in a small town, graduated from Grinnell College in Iowa, and taught English in North Carolina before moving to Arlington in 1971 with her husband Calvin, a lawyer who was President Ford's budget director and Federal Trade Commission chairman. They bought a house in McLean the following year. The Colliers have two children in the county schools, and one graduate of them.

Collier says her major interest on the board is in making sure the focus on children does not get lost amid deliberations about policy. Her greatest concern is that Fairfax County's size -- the system is the 10th largest in the country -- sometimes endangers that.

"We have to make sure each child is treated as a special individual and not lost in the crowd," she said.

"She is very sensitive and interested in kids themselves," said Marlene Blum, a longtime School Board watcher who has served on numerous school and county commissions. "It's important for School Board members not to lose sight of that."

Collier is an ardent fan of small classes, and is widely seen as being a major force behind the School Board's lowering of class sizes. In recent years, the board has reduced class sizes in the lower elementary grades and in "special needs" schools with large numbers of students who are poor, members of minority groups, immigrants or transient. Next year's proposed budget would reduce the pupil-teacher ratio in kindergarten classes. Within the limits imposed by lack of available classrooms, Collier wants more done.

"What citizens look for is that small class size and that individual attention," she said. "That's the one area where we are not competing with private schools. We need to improve on that."

Parents give Collier much of the credit for the School Board's recent vote to compress a three-year program to replace aging school buses into a two-year effort, even though it required asking for more money from the Board of Supervisors.

It was under her chairmanship that the board hired Superintendent Robert R. Spillane, who came last July from the superintendent's job in Boston. The board decided to hire him after Superintendent William J. Burkholder, stung by public criticism of the board's $157,000 pay offer to him, decided to retire.

Her board also voted to redraw high school boundary lines in much of the county in 1984, began a program to improve minority student achievement and test scores, expanded the county's program for gifted students, opened a science and technology high school, and cracked down on student drug and alcohol abuse.

Collier attends so many school meetings and sessions where she represents the School Board that she jokingly told her husband recently that her first free weekend to accompany him on a business trip is in March. Getting out and about is one of her strong points: "I see Mary as a person I can call up and talk to," said Catherine Belter, a local PTA activist who is president of Virginia's state PTA. "She's very accessible."

But her view that leadership means consensus-building does not mean she shrinks from tough issues, according to those who know her. When state Sen. Clive L. DuVal II (D-Fairfax) declined an invitation to the board's annual legislative dinner with a letter blasting some members for allegedly politicizing their jobs, she called him up to argue about it.

"She hits things head on," said Joy Korologos, the board vice chairman.

Said Blum: "She does like to keep the peace. But anybody who thinks that's all there is is making a big mistake." Blum cited her vote in favor of closing Fort Hunt, which displeased many in that neighborhood and prompted an unprecedented vote by two Republican members of the Board of Supervisors April 8 against her reappointment.

Falck said there was "no real threat to Mary's reappointment," and that that vote "was more for show than it was for blow." But others cite it as one more indication that the School Board members face more political heat these days from the supervisors who appointed them.

Now, in the view of some who feel she may not always take a strong stand on money matters before the supervisors, her leadership skills face a tough test. As the board approaches a vote on its proposed 1987 budget Wednesday , teachers are staging a work slowdown in support of a bigger across-the-board wage hike than Spillane recommended. The county PTA and several other civic groups support them; hundreds of students have staged sit-ins to back their faculty. Some of the strongest parent supporters of a bigger teacher pay increase are from her neighborhood.

Yet the Board of Supervisors, which pays the bills, appears less interested in an across-the-board raise than in pay hikes directed at specific groups of teachers, such as science faculty or the "best" teachers, with the method of choosing them yet to be determined. Spillane favors that approach, too.

And Collier, perhaps giving a clue to how she will vote on the issue, said Fairfax County residents are "willing to pay excellent salaries, but you don't get there by across-the-board increases. If we're going to attract people, we need to focus on those parts of the system that will attract them."

Keeping everybody happy -- or at least calm -- won't be easy.

"That is the hot seat that she sits on," said Kevin Bell, who heads the county Council of PTAs. "It's not an easy seat to be sitting on."