The Fairfax County School Board voted last night to convert Fort Hunt High School into an intermediate school, ending months of emotional debate in the eastern part of the county that galvanized communities into action aimed at preserving their schools.

The 6-to-4 decision was greeted with tears by parents, students and teachers from Fort Hunt and smiles by many from Groveton High School, which was threatened with closure.

Partisans of the two schools largely made up a crowd of about 500 in the auditorium of Fairfax High School where the board held its meeting.

The issue of school closings has been emotional and volatile in Fairfax where high schools -- more than any other institution -- are the focus of neighborhood life. The Groveton-Fort Hunt battle was especially intense because it affected some of the oldest and most established neighborhoods in the county.

The decision largely conforms to alternate recommendations made two weeks ago by School Superintendent William J. Burkholder, whose first choice was to close Groveton High. Ninth graders who would have gone to Fort Hunt will go to Groveton High instead. In the 1986-87 school year all Fort Hunt High students will switch to Groveton and Fort Hunt will become an intermediate school.

One of the goals of closing or changing the use of schools in the eastern end of the county was economy; schools there are losing enrollment while school construction is needed in Western Fairfax where thousands of families with children are settling in new homes.

Other considerations involved the quality of education. Larger schools resulting from consolidation can offer more programs.

Peter H. Brinitzer, chairman of the Neighborhood Schools Coalition of the Fort Hunt Area Inc., said he was "terribly disappointed and shocked." But he said he will do his best to make the plan work and keep his community together.

Lisa Keepe , a Fort Hunt freshman, said she was not happy with the decision and that many Fort Hunt students are determined not to go to Groveton.

"Groveton students have never gotten along with Fort Hunt students," she said.

Shifting to a private school or moving from the area apparently are the only alternatives open to the Fort Hunt students.

Paul G. Douglas, Groveton principal, said, "I feel the ball is really in our court now. We will have to get on with the job of mixing the two student bodies."

He said he plans to meet with Groveton students and teachers during this morning's first period class to discuss how to make Fort Hunt students feel welcome.

Deena Pettit, a Groveton junior, said she felt relieved by the decision. "But looking around and seeing all the tears of the Fort Hunt students makes me very sad."

School board members said the vote which came after many public hearings and long discussions, was the most difficult they had ever faced.

Voting for the proposal were Vice Chairman Carmine C. Caputo, Katherine Hanley, Anthony T. Lane, Laura L. McDowell, Robert Frye and chairwoman Mary E. Collier. Opposing were Joy Korologos, Anthony Cardinale, Olivia H. Michener and James W. Kitchin.

"I believe there is no one who is not physically, psychologically and emotionally drained by this exercise, which has taken practically all of our energy for the past six months," said Brinitzer.

Although the fight was bitter at times, some constructive things came of it. Both sides agreed it was a political education for students, many of whom spoke for the first time before the School Board, wrote impassioned speeches, and shared a new closeness with parents and faculty.

This pulling-together was particularly evident at Groveton High, where some of the county's richest students mix with some of its poorest on a sprawling, three-building campus.

There, students, parents and faculty pulled together for the first time in recent memory. School supporters raised more than $8,000, held rallies, and wrote reams of protest letters.

At nearby Fort Hunt, parents and supporters put together an an aggressive, well-financed and highly organized campaign.

At first, they lobbied to keep all neighborhood schools open, but later concentrated on saving theirs. During the course of their fight, the comfortable and homogeneous Fort Hunt community raised almost $15,000.

In other action, the board unanimously approved a five-year $151.9 million capital improvement plan, starting next year, including construction of two 21-room elementary schools, two 32-room elementary schools and one 1,000-student intermediate schools.

In an action unrelated to the eastern Fairfax school closings, the board voted to rearrange the boundaries of Robinson Secondary School southwest of Fairfax City to relieve overcrowding.