The Montgomery County Board of Education last night postponed a decision on the future of Montgomery Blair High School in Silver Spring until next November after board elections have been held.

The move came after the board rejected for the second time a proposal to change the school's attendance boundaries to draw more students, especially whites. Blair, with an ethnically diverse student body, is losing students as a result of board decisions to close several feeder schools, and it has become the object of debate over issues of diversity, racial balance and autonomy.

Last night board member Blair Ewing proposed that the attendance boundaries be changed, saying, "No matter what else the board does, the failure to extend the boundaries . . . will be perceived in the Blair community as having failed to deal with the real problem and will have doomed Blair to the perception of being an ineffective institution."

He was joined by member Elizabeth Spencer, but the move was defeated by the votes of Suzanne Peyser, Eleanore Zappone and Joseph Barse. Carol Wallace abstained and Marian Greenblatt was absent.

The board then voted unanimously to ask Superintendent Edward Andrews to evaluate the academic program at Blair and report to the new board in November. The present board generally has a 5-to-2 conservative majority. Four of the seven board seats will be up for election in November, including three now held by conservatives.

Options mentioned for Blair are closing it, bolstering it with stronger academic programs, turning it into a so-called magnet school concentrating on the performing arts or drawing more students through attendance boundary changes.

The school board made the last of its often bitterly contested school-closing decisions earlier yesterday, voting to close Kensington Elementary School this spring and send its students to Parkwood Elementary.

Before that vote, Ewing said, "I think we should make it clear that neither of these schools Kensington and Parkwood has failed in offering an extraordinary educational program. But we are left with the fact that it is also extraordinarily difficult to continue to offer good academic programs when enrollment falls to the point projected."

Every board member except Wallace voted to close Kensington, with the majority citing transportation problems and alternative uses for the Kensington school as reasons.