A silent alarm system installed by Metro two years ago after one of its bus drivers was raped has saved a driver from suffering the same fate, D.C. police reported yesterday.

A 32-year-old driver stopped her Metrobus at Eighth and D streets NE at 5 a.m. Sunday when a man wielding a pistol jumped into the bus, put the gun next to the driver's head, told her that he planned to rape her and ordered her off the bus, according to D.C. police.

The woman triggered a secret, silent alarm that alerted Metro headquarters. The driver also flipped a switch that turned on a set of flashing lights on top of the bus -- a signal that the driver was in trouble.

Metro transit police dispatched a patrol car and also called D.C. police for help.

The driver got off the bus and was forced toward a nearby car. When she got near the car, she grabbed the gunman and began struggling with him, police said. D.C. officers arrived while the two were wrestling in the street. Police arrested Richard McDew, 39, of the 400 block of E Street NE and charged him with assault with a dangerous weapon. A .38-caliber handgun was taken from McDew, police said.

Dennie Stewart, deputy transit police chief, said the silent alarm system has been used "extensively" since it was installed in 1978 after a bus driver was raped and her coworkers staged a one-day, wildcat strike to demand better protection for drivers. The alarm alerts Metro as to which bus the signal is coming from and then officials can determine where the bus is likely to be at a specific time.

Stewart said the system is used "about once or twice a week" by drivers who want police help in dealing with a problem on buses, usually rowdy riders.