THE BRONX - About 300 Parkchester residents gathered yesterday at a town hall meeting to voice their concerns about inadequate security in the neighborhood and to demand action. The residents' No. 1 complaint is the absence of security guards at three underground parking garages in the area. They say the lots are filled with blind spots, open doors and dark areas which could serve as perfect locations for crime. Between July and August, the parking garages lost all of their 24-hour security guards, leaving the lots unprotected except for a patrol truck that drives through the garages at different times, according to tenants.