Hundreds of workmen and machines struggled yesterday to clear out a torrent of Potomac River water that seriously disrupted Washington's Metro subway system as officials said they hoped to restore full service by Monday morning's rush hour.

"Our goal is to get ready to run by Monday if it is humanly possible," Metro General Manager Theodore Lutz declared as he toured the water-drenched station at L'Enfant Plaza."We have a fighting chance."

If trains can't run normally on Monday, Metro officials said they would restore many of the bus routes that were curtailed last month after the opening of Metro's Blue Line.

Yesterday, all trains on the Blue Line coming from Virginia were forced to stop at the Federal Triangle station. The seven stations at the eastern end of the line - from Stadium-Armory to the Smithsonian - all were closed as workmen tried to clear out water that entered the system Thursday evening when a barrier gave way at a construction site on the Southwest waterfront.

Yesterday thousands of commuters had their trips disrupted even though Metro ran shuttle buses over most of the route the trains usually follow.

As of last night, Metro officials said several inches of water still covered about a half-mile of track from the L'Enfant Plaza station to the station at Federal Center Southwest, 3d and 3d Streets, SW.

But they said pumping operations and reconstruction of the broken riverfront barrier were preventing any more water from entering the system. They said they hoped to have all water off the Blue Line tracks by today, but when service can be restored depends on what damage there may have been to the electrical circuits that provide power for the trains and signals to control them.

"We hope there hasn't been any extensive damage," said Metro community relations director Cody Pfansteihl, "but we can't be sure until it's all dried out."

Water started entering the subway system about 7 p.m. Thursday through a break in a steel-plated barrier on the bank of the Potomac River near 9th Street SW and Maine Avenue. (The barrier is called a cofferdam.) After passing through two other nearby barriers, it poured through a half-mile tunnel of the subway's unfinished Yellow Line and reached the L'Enfant Plaza station, at 7th and C Streets SW about four hours later.

The accident occurred where the Yellow Line underground tunnel from L'Enfant Plaza is to join two sunken concrete tubes that will carry trains about 900 feet across the bottom of Washington Channel.From there the line goes above ground on Haine's Point, crosses the Potomac on a newly built bridge and joins up with the Blue Line subway again at the Pentagon.

Eventually, the line is planned to run up the Seventh Street corridor to College Park and Greenbelt in Prince George's County, but no funds have been appropriated to extend it beyond 7th and G Street NW.

The line is not scheduled to open until late 1980, and officials said yesterday that the accident will probably have little impact on that timetable. However, whether the line will ever be completed is now being studied as part of an "alternatives analysis" about Metro's future.

An official of Bechtel Engineering Associates, which is supervising the construction for Metro, said the steel wall of the cofferdam may have been damaged when it was being driven into hard soil along the river bank.

Pfanstiehl said there had been some seepage through the wall before but it had been controlled by pouring more concrete. On Thursday evening he said, "it got ahead of them," although 11 men who were working behind the barrier had enough time to climb out safely.

All Thursday night and Friday a parade of large trucks dumped rock, dirt and gravel in an effort to build up the second barrier about 30 feet from the shoreline, and stop the water from coming any farther inland. Large pumps were also operating, and officials said the amount of water in Yellow Line tunnel was decreasing.

Workmen built another barrier with sandbags at the spot just before where the Yellow Line tunnel enters the L'Enfant Plaza station. By yesterday evening they had succeeded in reducing the amount of water raining down on the Blue Line that crosses below it.

Pfanstiehl said water was being pumped out of the Blue Line several yards east of the Federal Center Southwest station, which is the lowest point on the line, and being sent out through the District's sewer system.

No estimate of the cost of the flood was available yesterday, but Pfanstiehl said repair work would have to be paid for by the contractors who are building the river tunnel, a consortium of firms called Perini, Horn, Marrison-Knudsen.

So far contracts for the truncated part of the Yellow Line, from 7th and G Streets NW to the Pentagon, total $38.9 million, of which $21 million worth of work has been completed, according to Metro records.

Along the waterfront the pilings of the coffer dam go about 60 feet below water level, and the pressure is thousands of pounds per square foot. That is where the break occurred.

On Thursday night when they learned about the break, Metro officials turned off power and closed the Blue Line about 7:30 p.m., a half-hour earlier than usual.

Yesterday Pfanstiehl said that if water had reached the line while electric power was on the third rail carrying the electricity would have sparked and been disabled by a short circuit. Any trains on the line, would have stopped, he said.

For thousands of commuters the morning rush hour was turned into a torment by the disrupted subway service, and the trip back home seemed just as bad.

Many morning riders complained that Metro personnel did not tell them that trains would go no further than Federal Triangle and gave poor directions there about where to catch buses for the rest of their trip.

In the evening, riders were charged 50 cents for the shuttle bus from the closed subway stops to Federal Triangle - and many complained about it.

"I thought they were running the shuttle bus as a convenience to make up for the inconvenience of the train breakdown," said Jo Strada of Northwest Washington. "I can't believe Metro is doing this."