A lawsuit contesting the closing of Fort Hunt High School drew more than 100 supporters to a Fairfax County courtroom yesterday on behalf of an institution they call the center of their community's life.

The Circuit Court suit challenges the County School Board's votes in March to turn the 21-year-old school into an intermediate school and send its 1,260 students to Groveton High School. The merged school, scheduled to open in the fall, will be called West Potomac High. The board acted because of declining enrollment in the eastern part of the county.

The lawsuit by Fort Hunt parents argues that the board's action was improper because West Potomac High will be overcrowded and because the board failed to consider any action involving nearby Edison High School. Testimony is expected to conclude today.

Many of the Fort Hunt supporters sported green and gold lapel ribbons in court yesterday to show their school spirit.

Frank W. Dunham Jr., the attorney representing them, said in his opening remarks that many parents bought homes nearby so their children could attend Fort Hunt, a school with a distinguished record of academic and other achievements. "They have come to believe there is something special about their school," he told Judge Richard J. Jamborsky, who is hearing the lawsuit without a jury.

The School Board, he said, believes schools are "almost like McDonald's: You can go to any one of them and get the same hamburger."

Witness Paul Dux, a Fort Hunt parent, likened the school to a New England town green. "It serves not just as an educational facility, but also as a social nexus for the community."

Witnesses testified that West Potomac High will house 2,400 students in a building designed for 1,900, necessitating the use of temporary mobile classrooms and the conversion of teachers lounges, an art gallery and other areas into class space.

Gerald A. Fill, the Fort Hunt area's former School Board member, testified that Sandra L. Duckworth, the area's county supervisor until last year, pressured the school system into leaving Edison off a list of locations considered for merger or closing.

Thomas J. Cawley, the School Board's attorney, countered that there will be room for all students in "the new and greater West Potomac" because of school modifications. "It's a school that's going to work," he said.

Although he did not address the Duckworth and Edison issue directly, Cawley said "there's no question that other solutions were possible. But . . . the essential thing is that the School Board did not act arbitrarily or capriciously."

Judge Jamborsky, recognizing the strong feelings of many in the room, tendered a friendly warning that applause and other audience response would not be tolerated. But he also asked each witness and lawyer to speak loud enough to be audible in the back of the room, and urged spectators to raise their hands if they could not hear.