An electrical transformer at the D.C. Municipal Center broke down yesterday, cutting off power for more than three hours to police headquarters and several other city agencies and trapping workers and visitors briefly in several stalled elevators.

Power at the six-story building, on Judiciary Square at 300 Indiana Ave. NW, went out at 10:56 a.m. and was restored at 2:04 p.m., according to the Potomac Electric Power Co. The cause of the disruption was not determined immediately.

During about an hour of that period, starting at noon, an unrelated incident forced the cut-off of power on a downtown segment of Metro's Red Line, interrupting subway service between the Judiciary Square and Dupont Circle stations. Partial service was restored at 12:57 p.m. and full operations at 1:18, Metro reported.

The Municipal Center transformer breakdown cut off computers and lights in police, motor vehicles, public health and finance offices located in the building. Issuance of drivers' licenses and car tags came to a halt.

Standby generators were turned on, providing power for police communications, the police chief's office and the mayor's emergency command center.

Elevators caught between floors were lowered manually to the next floor, where passengers could get out. There were no major problems, officials said.

The Metro shutdown came after insulation on a cable feeding power into a trackside third rail between Metro Center and Farragut North stations overheated and began smoking, a spokesman said. Power to both tracks was immediately cut off and an emergency bus "bridge" was provided to carry train passengers between Dupont Circle and Judiciary Square.