The Montgomery County School Board, midway through its decisions on school closings, voted last night to shut down three more elementary schools in the Rockville and Wheaton areas in June 1983.

The board's decision brought to 18 the number of schools it has designated for closing during the past two weeks.

The latest to be so designated are Connecticut Park Elementary, Rocking Horse Road Elementary and Brookhaven Elementary.

Last night's votes were relatively free of controversy. In one instance, the board opted against closing a school with a high minority enrollment, Harmony Hills Elementary, and chose instead to close Brookhaven. Superintendent Edward Andrews had reminded board members that Harmony Hills, with roughly 40 percent minority student population, had the largest minority enrollment of any school in its area.

Board member Blair Ewing cited that reminder and suggested that the proposal to close Harmony Hills be rejected to avoid setting a pattern of segregation in school closings.

Board member Marian L. Greenblatt suggested closing Brookhaven instead of Harmony Hills, citing fiscal reasons and the physical plant as well as the minority issue that Ewing raised.

The board postponed closing Lucy Barnsley Elementary by voting against a resolution that would have shut down the school in 1986. Board members who voted against closing Barnsley noted that students attending it had recently been consolidated from other schools in the area and said it would be unfair to name the school for closing five years ahead of time.