The Metro Board voted yesterday to refit about 150 of its new buses with windows that will open when--as expected--the air conditioning breaks down next summer.

The vehicles, the most modern in Metro's 1,700-bus fleet, have been dubbed "steambaths on wheels" when full of summertime passengers. But rather than take them out of service when the air conditioning systems aren't working, the board agreed to spend $475,215 to install new windows that can be opened from the inside.

The modern buses were built with sealed windows to prevent people from evading fares by receiving transfers from passengers, and to make the air conditioning more efficient by eliminating hot air drafts from outside.

Unfortunately for Metro and its passengers, the air conditioning systems continually fail during hot weather and riders stew inside.

The lone opponent of yesterday's funding decision was Montgomery County board representative Cleatus Barnett, who argued that money should be spent instead to improve the air conditioning on the new buses -- the sleek, dark-windowed models and the articulated, accordion-style models.

His argument was countered, however, by Theodore Weigle, Metro's assistant general manager for operations, who said it would cost much more to try to fix the air conditioning than to install windows that can be opened.

In preparation for its expected decision next month, the board also was given staff-prepared options on the routing of Metro's Green Line into Prince George's County.

The subway system's original 1968 Master Plan showed the line ending at Branch Avenue, but the board, following a vote by the Prince George's County Council, switched in 1980 to a southerly line ending at Rosecroft Raceway. A federal appeals court subsequently ordered public hearings on the Green Line route, which took place in the county and in the District this past June.

The staff recommended that the District segment of the Green Line be aligned from the Waterfront Station in Southwest and proceed through an Anacostia Station located at I-295 and Howard Road.

But the staff, believing that the final determination of the Green Line route -- either to Rosecroft or Branch Avenue -- will be a political decision, stopped short of recommending any alignments beyond the Anacostia station and into Prince George's County.

The staff did outline three alternative route segments for the Green Line between the Anacostia station and the District/Prince George's County line.

Under one option, the route would pass onto the grounds of St. Elizabeths Hospital and continue to the Branch Avenue terminus. In a second option, it would go from St. Elizabeths to Rosecroft. In the third, the route would run along the southwest side of Suitland Parkway to a Branch Avenue terminus.

Depending on which route is selected and where the Green Line ends, the construction could cost between $240 to $370 million, according to Metro estimates, which were made to reflect 1987 dollars.

In other board action, the board's chairman, the Rev. Jerry Moore, sent a letter to Fairfax County Board of Supervisors Chairman John F. Herrity requesting the county's share of second quarter operating assistance. The county had voted to withhold funding when Metro pushed back plans for a fare increase from January until April. But the board has since adopted resolutions designed to allay the county's concerns about lost revenue during the fare hike delay.

Moore also announced plans to lead a five-member Metro delegation on a trip to Pistoia, Italy, to inspect the manufacturing progress of newly ordered rail cars. The trip is tentatively scheduled for Nov. 6-13 and is expected to cost about $8,750, according to a Metro spokesman.

The board also discussed a planned Nov. 7 disaster drill, simulating a train derailment and fire under the Potomac River between the Rosslyn and Foggy Bottom stations, that will test new emergency rescue equipment.