Metrobuses will start using the new Pentagon bus terminal Monday as preparations continue for the opening of the Metro subway's Blue Line Friday.

The bus terminal, which has 22 saw-tooth bays, is located on the southeast side of the Pentagon and sits directly on top of the new Pentagon Metro station. When the Pentagon subway stations opens Friday, two escalators will carry riders transferring from the buses and the trains. A third set of escalators links the Metro station with the Pentagon shopping concourse.

The new bus terminal will be used between 6 a.m. and 8:30 p.m., Monday through Friday, the hours that the trains will be running. On weekends and during the night when the trains are not running, buses will continue to use the old Pentagon bus tunnel B, with stops at platforms B6 and B7.

The new bus terminal was constructed in conjunction with the metro station and will become a major public transit hub for Northern Virginia as Metro's start-up plans proceed.

Many Metrobus routes that now continue into the District of Columbia will be terminated at the Pentagon in the months to come. Although no changes will be made with the inauguration of subway service Friday, some buses that travel through North Arlington will be terminated at the Pentagon beginning July 17.

The big change for the Pentagon comes Sept. 4, however. Than, virtually all the buses that use the 14th Street Bridge to get to the District of Columbia will either be routed through the Pentagon or terminated there.

The Pentagon itself, with 24,000 employees, has the highest concentration of bus commuters of any single employment location in the metropolitan area. Almost half, or 11,000 employees daily, get to work at the Pentagon by bus.

Most of the others get there by car pool, because the Pentagon lots are one of the federal locations in the area where car-pooling requirements are genuinely enforced.

The Pentagon subway station will be opened during the week starting Monday, although the trains will not be running scheduled service and will not board or discharge passengers there. However, those who wish to prepurchase Farecards - the magnetically encoded ticket that all subway riders will have to use starting Friday - may do so at the Farecard vending machines between 6 a.m. and 8:30 p.m.

Farecard vending machines will also be open to the public at three other Blue Line Metro stations next week before rail service begins. The Crystal City and Rosslyn stations will be open Tuesday, Wednesday and Thursday from 11 a.m. to 6 p.m. for Farecard vending; the L'Enfant Plaza station will be open Monday through Thursday from 11 a.m. to 6 p.m.

Metro will continue to give demonstration rides on the new Blue Line on Monday and Tuesday for Maryland residents. Users can board at only one station: Stadium-Armory, between noon and 4 p.m. Monday and from 9:30 a.m. to 4 p.m. Tuesday. Trains will run every 10 minutes. Riders will not be permitted to leave the train and must take the round trip from Stadium-Armory to National Airport. The Stadium-Armory station is on 19th Street SE between A and C Streets SE.