An apparent clog in a sewer forced billows of steam out of manholes in a section of Georgetown last night, flooding buildings and causing the evacuation of about a dozen people from a residential hotel.

Dozens of firefighters, engineers and utility workers converged on 29th and K streets NW shortly after 6 p.m. after puddles of condensed steam set off alarms in an underground garage and nearby row houses.

Workers cut power and water supplies to the Georgetown Harbour Mews hotel and nearby buildings in an attempt to locate the source of the problem and prevent an explosion. About a dozen hotel residents were evacuated.

Fire officials initially said the water and steam came from a leak in a 29th Street power plant that supplies heat to the White House and about 100 other federal buildings.

But Roland Miller, a supervisor with the General Services Administration, later said steam and hot water from the plant began leaking into the garage and row houses across 29th Street because the sewer system was backed up. "The problem won't stop until the D.C. government unclogs the sewer system," he said.

Capt. Ted Holmes, a fire department spokesman, said about two feet of water collected in the garage and row house basements before leveling off about midnight, shortly after the power plant shut down some of its operations.

The normally quiet section of Georgetown was still bustling early today, with firefighters and utility workers working by floodlight to pump water out of the basements. Because the buildings house commercial establishments, no one had to be evacuated.

K Street was closed to traffic between 25th and 31st streets NW, and 29th Street was blocked off at M Street NW.