The Metro board yesterday voted to buy 115 new buses from General Motors for $10.8 million despite reservations of some board members about the fact that the windows on the buses are sealed closed.

The board's action, taken after two weeks of study, came at the 11th hour. The low bid from GM would have expired before the next board meeting.

Two weeks ago, the board rejected, then reconsidered and delayed action on the bid after D.C. board member Jerry A. Moore questioned the efficacy of buses with windows that remain closed. It gets hot in Washington, he pointed out, and the air-conditioning on buses does not always work.

The problem is that the buses come only with sealed windows.

Officials from GM appeared at the board meeting yesterday to assure members that air-conditioning and venting problems on the new buses had been worked out. "If the air-conditioning fails, you still have fans," said GM's Robert Hauser.

Moore joined the unanimous vote to accept GMs' low bid, but promised THAT "I will be watching very carefully to see how these buses perform." The first of the buses should be on Washington streets by the end of the summer.

Walter Frankland, the new Metro board member from Arlington, lost no time pursuing his favorite cause. Two minutes after he was sworn in, Frankland asked the Metro staff to tell him how much it would cost to operate a Metro subway system that was only 60 miles long instead of the planned 100 miles.

Long-time board member Cleatus Barnett, who has been reappointed from Montgomery County, said that Frankland's request "seems to be asking for the preparation of a bobtailed system. That would be a diversion of staff time." The board, througout its history, has beat all attempts to do anything that would appear to support truncating the planned system.

Moore, acting chairman, noted that staff traditionally answered queries from board members and discussion ended there.

In other matters, Montgomery County told the board that 210 more parking space now are available near the Silver Spring Metro station -- 180 of them for all day parking and 30 for mid-day parking. All-day parking stickers, costing $35 a month, can be obtained by calling 565-7693. The lot is immediately adjacent to the north entrance of the Silver Spring station.