Frustrated officials muttered darkly about the "Friday the 13th" blackout as some government employees were given the rest of the day off. Pepco, the utility provider, reported power was restored to all customers before 11 a.m.

The power went out at 7:25 a.m., idling arriving office workers outside darkened workplaces. Two small fires on Metro tracks snarled morning subway commutes. It wasn't clear whether the fires were caused by power problems, which have been blamed in the past for track fires.

At one point, Pepco reported more than 18,000 customers without power. A single office building is one customer, and it was unclear how many affected were residential users, and how many were commercial customers.

The White House went smoothly to backup power.

Pepco said the blackout occurred because a switch failed on a transformer at a substation in the Chinatown area. Spokesman Bob Dobkin said it was unclear why that occurred.

The outage cast Pepco's downtown headquarters into darkness though a generator provided power for some lights and phones.

"We certainly know what our customers are experiencing," Dobkin said at the time.

Elsewhere, traffic lights were knocked out, contributing to accidents in which two pedestrians were injured, said Alan Etter, a spokesman for District of Columbia fire and emergency medical services.

"Friday the 13th certainly is living up to its reputation," Etter said.

Metro riders experienced long delays after two fires at the Metro Center station, which forced trains to share a single track. The first fire was reported at 7:24 a.m. and the second at about 9:50 a.m.