The Montgomery County Council and the American Civil Liberties Union yesterday sent sharply critical letters to the county school board urging members to review the effects of their actions on low-income and minority citizens.

The board received the letters just as it was preparing for its final session of voting on school closings and boundary changes. On Monday night, in response to community pressure, the board voted to preserve elementary school groupings in the Takoma Park area that were established to improve racial integration.

In addition to the council and the ACLU, the National Conference of Christians and Jews also criticized the board yesterday for decisions that it said will have an adverse effect "far beyond the walls" of county schools, on racial balance, housing patterns and business and employment in the county.

The most critical message to the board came from the ACLU, which questioned why Superintendent Edward Andrews' master plan recommended school closings and boundary changes without considering racial balance as a primary screening factor. The ACLU said the board has an opportunity to improve integration in the county schools during the school closings process, but the failure to consider racial balance as a principal ingredient "could perpetuate existing pockets of segregation and create new ones."

Further, the group charged that decisions on schools have been made "so rapidly that the concerned public has been utterly unable to submit and prepare meaningful comments."

The letter from the County Council, more moderate in tone, said council members "sympathize with the board's difficulties" in making "these difficult decisions" on school closings.

"At the same time," the letter states, "we are concerned with the impact of these decisions on communities, particularly those with high minority populations or economic problems."

The letter, signed by council president Ruth Spector and addressed to school board president Carol F. Wallace, urges the board "to review the decisions you have made with the utmost care."

"Because negative perceptions have arisen about some action of the Board of Education, it is very important the the board provide the council and public a full explanation of the decisions made . . .especially) where those decisions have departed from the recommendations of the superintendent," said Spector's letter, which the council drafted late in the afternoon after council member Esther P. Gelman presented a draft version.

The ACLU letter said that preliminary findings of a study it is conducting show that the school closings affect minority students disproportionately. Those preliminary findings were based on the superintendent's plan and do not take into account areas where the board has deviated from that plan.

In its decision Monday night, the school board gave in to strong community pressure in the Takoma Park area and agreed to preserve two groupings of elementary schools that were established five years ago as part of a school integration plan.

The decision coincided with a recommendation of the superintendent. He originally had proposed splitting the two groups of elementary schools in Takoma Park, returning all five to a kindergarten through sixth grade structure. Last week he proposed changing that plan, and called on the board to leave the schools as they are, divided into two groups with two schools serving kindergarten through third grade and three serving fourth through sixth grade.

When the board majority voted last week to close Rosemary Hills Elementary in Silver Spring, now paired with Chevy Chase elementary, one of its principal arguments was that schools serving kindergarten through sixth grade are better educationally.

In supporting the paired schools in Takoma Park on Monday, board members said there was more community support for such a structure in the Takoma Park community than in Rosemary Hills and Chevy Chase.

Even with the preservation of paired schools, the Blair High School area, of which Takoma Park is a part, will have a minority student population above its present level of 63.8 percent. Under school board guidelines, the school system must investigate ways of attracting white students to schools where the minority enrollment is higher than 60 percent.

The board rejected one of the superintendent's proposals earlier this month that would have sent more white students into the Blair area to help the racial balance problem.

The board voted last night to close Brookview Elementary and to send students living in the area to Cresthaven Elementary. Those students would go on to Springbrook High School. Students entrolled at Brookview who live further south of the Beltway in the New Hampshire Estates area, which is overwhelmingly minority, will remain in the Blair High School area.

The board has won a reprieve on one civil rights challenge filed last year by parents from the Congressional Elementary school. They claimed that the board granted a rezoning petition that worsened racial balance at the school. The Department of Education, in a letter to Superintendent Andrews last week, said there was "insufficient evidence to constitute a violation" by the board.