A Potomac Electric Power Company cable feeding electricity to the Eastern Market Metro Station failed yesterday and forced Metro to close down four stations on its Blue Line through the evening rush hour.

Metro officials said they would restore full train service from the Stadium-Armory station this morning either with a repaired Pepco cable or with an emergency gasoline generator. If the generator has to be used, the Eastern Market Station will remain closed.

The four stations that were closed after the 11:15 a.m. power failure - Capitol South, Eastern Market. Potomac Avenue and Stadium-Armory - are on the easternmost leg of the Blue Line and serve as major transfer points between the subway and bus routes into Prince George's county aid Southeast Washington.

Metro ferried subway riders to those stations on free shuttle buses it ran from the Federal Center SW station. But Federal Center was never designed to take the kinds of commuter loads that resulted from it becoming a Metro terminal, and hundreds of people were backed up at one point on escalators and behind the inadequate automatic fare-collecting equipment.

"Blame this on Pepco," one harried Metro employee said to an irate patron.

Pepco, it must be reported, is only half to blame. Two 13 kilovolt feeder lines carry electricity into the Eastern Market Station. One of them "faulted," in Pepco terminology.

The other, the back-up line, could not be used because the Metro transformer that would reduce that high-level current down to station size is cut for repairs and is not expected back for a week.

"If you've ever seen a classic application of Murphy's Law, this is it," said Metro's Joseph Greenway, who is in charge of train controls and signal systems.

"On one end I've get a good feeder going into a nonexiestent transfer, and on the other end I've got a perfectly good transformed but no power."

Murphy's Law holds that if anything can go wrong, it will, at the most inconvenient time.

The electrical failure did not affect the power for Metro's trains, but knocked out signals, the electronic message senders that control the trains, lights and such equipment in that station as automatic fare collecting systems.Also knocked out were the controls for the crossover at Eastern Market that lets Metro turn trains around at the end of the line.

With that crossover out, Metro had to close stations back to Federal Center - the closest operating crossover.

Service on the rest of the Blue Line was normal, Metro spokesman said.

The power outage was the second major interruption to subway service since the blue Line opened July 1, Service to seven Blue Line stations was cut for almost a week in August when a construction accident permitted water from the Washington Channel to flood the Blue Line at L'Enfant Plaza.

There also have been at least three fires, one wreck involving test trains, plus numerous mechanical difficulties with the new Metro cars.