Thousands of commuters on Metro's Orange Line were delayed during yesterday evening's rush hour when an electrical circuit overheated on a Metrorail car, forcing firefighters to shut down part of the line in both directions, authorities said.

No one was injured, but dozens of riders were trapped in the front car of the six-car train after a circuit on one of the cars behind it overheated about 6:45 p.m., Metro spokeswoman Marilyn Dicus said. The Vienna-bound train had just left the West Falls Church station.

The riders in the middle and rear cars were evacuated through the back of the train onto another, but the Fairfax County Fire Department would not allow riders in the front car to walk through the train to the back, Dicus said.

Fady P. Bassily, Metro's assistant general manager for rail service, said the evacuation was caused by an overheated circuit in the car's motor. No fire was involved, and the passengers were not endangered, he said. The incident halted all Metro service west of West Falls Church and slowed trains along the rest of the Orange Line.

The problem was quickly identified, but the train could not be moved until power was restored to the tracks, and fire department officials would not allow Metro to turn on the power until they were sure there was no danger.

Metro pulled the disabled train back to West Falls Church and unloaded the trapped passengers at 7:37 p.m. Full service was restored at 7:41 p.m.