Smoke in the brake system under one of Metro's subway cars interrupted service on the Blue and Orange lines for 50 minutes late in yesterday's morning rush hour, forced the temporary closing of the Smithsonian station and made thousands of commuters late for work.

The smoke, from a bank of resister grids, was suppressed by the D.C. Fire Department without incident, according to a department spokesman. There were no injuries. In the process, however, the electricity was turned off for both inbound and outbound tracks at the Smithsonian station.

That blocked service between 8:32 a.m. and 9:22 a.m. on both the Blue and Orange lines, which share the same tracks at that point. Some trains were run to the blockage and then reversed, but "most trains were held in stations," according to Anthony Stefanac, Metro's general rail superintendent.

That breakdown, combined with other difficulties on the Blue and Orange lines, gave the subway one of its worst rush hours in recent months. Passengers were asked to leave stricken trains at Farragut West, Metro Center and Potomac Avenue. An ill passenger caused another train to wait for nine minutes at the Rosslyn station.

The Potomac Avenue train, inbound on the Orange Line, had waited there while the fire department finished at Smithsonian. The train was unable to proceed after service was restored because the doors would not close. The passengers who had already waited for more than 30 minutes, waited some more while the stricken train was removed and another train brought in.

Smoking brake grids have plagued Metro's trains off and on since the subway system opened and are among the reasons -- along with the recently abated screeching -- Metro officials are taking a detailed look at the entire braking system. Balky doors are another long-running Metro problem.

Those difficulties will be high on the list of problems facing Joe H. Sheard, who was just named yesterday as new director of rail services for Metro. Sheard, who comes from the subway construction office, will get the opportunity to run what he helped build. He replaces Ralph Wood, Metro's first rail services director, who retired last week.