WASHINGTON (AP) _ The lights went out in much of downtown Washington Friday night, plunging the Washington Monument, the National Theater and scores of shops and office buildings from Georgetown to the Mall into darkness.

The local power company said a generating station across the Potomac River in Alexandria, Va., failed around 8:30 p.m. The power was restored shortly after 9:30 p.m.

The blackout brought the curtain down early on a performance of the musical ``Chicago'' at the National Theater, and on ``The Phantom of the Opera'' at the Kennedy Center.

Police lit flares at key intersections downtown, and cars creeped tentatively through the darkened streets.

The blackout affected some 10,000 customers in the Georgetown, Foggy Bottom, Mall and Tidal Basin areas. Some Metro rapid transit stations were affected.

Nancy Moses, a spokeswoman for Potomac Electric Power Co., the local utility company, said the problem stemmed from a failure at the Potomac River Generating Station in Alexandria, two miles south of National Airport. The airport was not affected.

The lights went back on after PEPCO switched to alternate sources of power.

Moses said the cause of the failure had yet to be determined.

Charlie Thomas, a park ranger at the Washington Monument, said several tourists were at the top of the 550-foot obelisk when the power failed. He said the tourists were guided by emergency lighting down the 897 steps to the base of the monument.

``Fortunately, the elevator was not loaded at the time,'' Thomas said.

A spokeswoman for the Secret Service, Lisa Risley, said that at the White House, ``None of the normal operations were affected by the power loss.''

The president was in Denver for the summit of the world's major industrialized nations. Barry Toiv, a spokesman for the White House in Denver, said the executive mansion has an auxiliary backup power system but he wasn't sure if it was activated Friday night.