Northwood High School, a Silver Spring institution and the last of 28 Montgomery County schools once slated for closing, should shut its doors as planned this June, the County Board of Education decided last night before a jeering crowd of the school's supporters.

In a 5-to-2 vote shortly before midnight, the board agreed to accept a proposal from Superintendent Wilmer S. Cody to close the 29-year-old school and send its 894 students to Blair, Kennedy and Einstein high schools.

A last-minute amendment by board member Sharon DiFonzo, who voted with board member Jeremiah Floyd to keep the school open, will allow students from Northwood's 1986 graduating class to choose which of the three schools to attend their senior year.

"If we are asking the class of '86 to give up their senior year," DiFonzo said. "The least we can do is let them transfer to any of those schools.

The vote to close the school came hours after the Board of Education listened to staff members outline projections of enrollment -- expected to grow by about 12,000 to reach 103,000 through 1990 -- and reviewed arguments offered last week by community members who wanted the school to remain open.

The decision capped months of debate by the school board and four years of fighting by the Northwood community, which had consistently and tirelessly researched and presented reasons why the school should remain open.

"You know, I hope we are wrong," said student government president Shawn Brennan, "I hope the things we said will happen -- overcrowding and those things -- won't because then things will be a mess."

Northwood had first been slated to close when the board voted in 1981 to close 28 schools in an attempt to cut costs and adjust to declining enrollments. In 1983, the board voted to delay the closing from 1984 to 1985.

Superintendent Cody reopened the question of the future for Northwood late last year during a preliminary review of school facilities. He said then that the board should reconsider in light of development in Montgomery County that would add to public school population.

In January, Cody submitted three proposals for the board to consider. Two recommended that the board retain the school, but Cody said the proposal he most favored -- because of fiscal constraints and educational needs -- would close the school.

The board held two hearings last week to discuss the superintendent's proposal and heard from dozens of residents from neighboring high schools who disagreed with the Northwood community's pleas.

Representatives from Blair, Kennedy and Einstein high schools questioned the feasibility of maintaining Northwood, a facility that needs major renovations, when better-maintained, larger schools could absorb the Northwood enrollment.

Northwood backers argued that the school, which has a capacity of 1,850, should be used to help alleviate overcrowding in those nearby schools and also retain what had been a vibrant center of their community since 1956.

In hours of testimony, they presented a plan to retain the school by adding students from minority programs at Blair High Schools and rearranging boundaries to include students from Kennedy, Einstein and Springbrook high schools. With those changes, the school would have served about 1,000 students, the minimum recommended under present school board policy.

Those arguments did not sway several board members including Blair Ewing, who had voted twice in the past to close Northwood. Last night he questioned the proposed juggling of Blair High's minority program and questioned whether the maintenance of Northwood would meet county educational standards.

"I'm convinced, in terms of being able to offer quality programs, we will do better with large enrollments," Ewing said.

Board member James Cronin agreed and added that "beyond being cost-ineffective, a small school is educationally deficient."

Board member Marilyn Praisner made one attempt to delay the board's decision last night by asking for a separate motion to reconsider Northwood again next year so it could remain open through 1986. Her request went unanswered by other board members.