Seven stations on the Metro Blue Line will remain closed today because workmen have been unable to clamp a steel lid on the giant leak that let water from the Washington Channel flood into the subway system Thursday.

"I have concluded that it is not an acceptable risk to the general public to reopen the subway" between the Federal Triangle and Stadium-Armory stations, Metro general manager Theodore Lutz said yesterday.

That means that for the third day of subway operations since the flooding occurred there will be train service through only 11 of the Blue Line's 18 stations. The Red Line between Dupont Circle and Rhode Island Avenue NE will operate normally. Augmented Metrobus service will be used to carry frustrated subway riders.

Lutz and Roy T. Dodge, Metro's assistant general manager for cconstruction and design, said they could not predict exactly when full service will be restored on the Blue Line, although they clearly expected it to be this week. They had originally hoped that the problem could be solved by yesterday.

As far as the stations themselves and the trains are concerned, all is back to normal. The stations that were flooded - L'Enfant Plaza and Federal Center SW - have been cleaned. Electronic circuits have been restored and several test trains have run on the tracks without a hitch, maintenance crews having worked through the weekend.

But there was still that leak that started when water breached three temporary barriers at a Metro construction site between the Flagship and Hogate's restaurants on Maine Avenue SW. Water from the Washington Channel then flowed through a completed but unused Metro tunnel to the L'Enfant Plaza Station, where it encountered and engulfed the Blue Line.

Lutz and Dodge said the flow of water from the channel into the tunnel had been "stabilized" and that pumps were slowly lowering the water level. But the flow from the channel "should be reduced more," Lutz said, so that there will be no infiltration.

Divers attempted yesterday to fit a steel plate, or bulkhead, to the entrance to the flooded tunnel. The plate was lowered into the water Sunday night, but a tight fit against the concrete face of the tunnel still had not been achieved by late yesterday.

Once that bulkhead is in place - and assuming there are no other leaks - water can be pumped out of the tunnel.

The contractor, a joint venture of Perini, Horn, Morrison and Knudson, also is planning to build two concrete plugs in the two tunnels from the channel to the L'Enfant Plaza station. But that cannot be done until the buikhead is secure.

Yesterday there were five feet of water at the point in the tunnels where the plugs will be poured, according to Harold McKittrick, project manager for the joint venture.

"I would recommend that they not operate until the plugs are in place," McKittrick said. He estimated it would take at least 12 hours for the concrete to "set up" after the plugs are poured. That could mean a delay running well in this week.

"I have not accepted the judgment" that the plugs are necessary for operations, Lutz said yesterday. But he was clearly unwilling to operate trains as long as seepage continued.

While the contractors and Metro officials held meetings and while divers attempted to fix the bulkhead in place, commuters seemed to get along pretty well.There were few difficulties reported or observed along the route of the Blue Line that was being served by free shuttle buses.

About 3,000 commuters used the bus shuttle in the morning, Metro officials estimated. Many of them transferred from the subway to buses at Federal Triangle. "I don't think it's been much of an inconvenience," said Elwood Titus, a biologist for the Food and Drug Administration.

There was some confusion. Commuters waiting for a ride at the Eastern Market station watched several Blue Line shuttles go by without stopping. They finally got a ride. Bus drivers were acting like bus drivers and waiting for the bell to ring before they would stop, but their passengers were acting like subway riders and assuming their conveyances would stop automatically.

As a bus from the Stadium-Armory station to the Federal Triangle rolled through the Southwest Mall area and past the L'enfant Plaza station entrance, a woman passenger fidgeted for a moment, then stood up and said to the driver:

"Excuse me, sir, are you stopping at L'Enfant Plaza? The last subway stop was back there and I was supposed to get off." The driver stopped and she got off.

The trains were running well, as they generally have been for the past two weeks. Metro officials are lamenting the fact that they were getting on top of several operational problems, such as sticking doors and balky trains, when the flood came.

Subway ridership is down dramatically, as would be expected. An average of 115,000 people had been riding the trains through last Wednesday. On Friday, the first full day of post-flood operations, only 81,676 people rode the subway.

The biggest single loss to Metro will be in subway revenue, Lutz said.

This is the second time there has been a flood in a Metro tunnel. The first time was Sept. 26, 1975, before any of Metro was open for operations. On that occasion rains from Hurricane Elosie raised Rock Creek above a cofferdam protecting a Metro tunnel. Water surged through the tunnel to the Dupont Circle station, where it was contained.

After that incident a concrete plug was placed in the tunnel near the Rock Creek excavation.

Why wasn't that done at L'Enfant Plaza before the dam broke? Dodge, when asked that question, said, "We thought we were secure with three lines of defense" - two barricades in the channel and the bulkhead itself.

McKittrick insisted that the bulkhead alone should have been adequate. There have been persistent problems with the integrity of the walls of the outer barricades, he said, but leaks had been plugged and contained regularly before the blowout Thursday night.