The few remaining restrictions on water use in suburban Maryland will remain in force until Wednesday or Thursday , the country executives of Prince George's and Montgomery counties announced yesterday.

By then, the officials said, the pumping capacity of the Washington Suburban Sonitary Commission's water system, which was drastically reduced last week after a fire crippled a major pumping station, should be back to normal.

At the moment, any outdoor water use by the 1.2 million WSSC customers in the two counties is forbidden, except between 9 p.m. and midnight.

Water conservation efforts last weekend continued to prove successful, WSSC general manager Robert S. McGarry noted - 100 million gallons were consumed on Friday, 135 million gallons on Saturday, and 123 million on Sunday.

On Wednesday, the day the major pumping station on the Potomac River was disabled. 172 million gallons were drained out of the system, severely depleting its reserves and prompting the county executives to put strict mandatory conservation measures into effect.

On Wednesday, according to Montgomery County information officer Charles Maier, the WSSC commissioners will meet to decide whether it is necessary to continue the restrictions.

As the prob lems stemming from the breakdown of the pumping system last Wednesday were gradually resolved, another water supply problem somewhat worse over the weekend. By yesterday the level of the Potomac River measured at the pumping station's intake had dipped slightly below 157 feet. That level (which indicates the river's height above sea level at that point) is the minimum at which water can be efficiently pumped out of the river and into the WSSC system.

In response, the WSSC yesterday carried out a plan, approved last Friday by the Army Corps of Engineers, to construct a weir - a small dam that usually is under water - just dowmstream from the pumping station's intake.

Helicopters were used to begin the construction by depositing gabions - wire mesh cages tilted with rocks - into the river 50 feet downstream from the intake.

The intermittent showers that fell throughout the area yesterday "weren't heavy enough in the river basin to make an appreciable difference" in the river's level, said Charles Chilton of the National Weather Service.

The mandatory restrictions that helped further the water conservation effort were still prompting sporadic complaints from some affected businessmen yesterday, but others continued to regard the water shortage crisis and its effects fatalistically, saying that no one was to blame.

As he surveyed his brown and withered stock yesterday William Burton, owner of Burton Nurseries of Hyattesville, complained that he had lost $10,000 to $15,000 because of the water restricions. "Junipers, pyracantha - you name it," Burton fumed.

Normally those plants have to be watered at least once and often twice a day, he explained. During the crisis, he did not water them Wednesday, Thursday and Friday.

Burton said that he could not understand why the WSSC had "no backup system" to continue the water supply when equipment is not functioning.

The WSSC does have extra equipment, including pumps, in reverse in case of malfunctions, but does not have an extra control panel, an elaborate and expensive device used in allocating water. To have one of these in reserve, WSSC officials have explained, would be roughly equivalent to a homeowner's buying a second house in case anything happens to the first one.

"The way I look at it the WSSC should be liable for my looses," Burton continued "I think we have a contract. They are paid to supply me water and when they don't do it, they should pay for the consequences."

Other businessmen were not so disturbed.

"I'm not interested in criticizing their decisions: I haven't looked into it that much." said James Harmon, director of administration for the Litton Industries plant in College Park.

Harmon said that the plant, which manufactures electronic equipment, lost money when it was forced by the WSSC to close down last Friday, but said that he didn't have enough information to say whether the WSSC's reasoning was valid.

"We've had pretty good service," Harmon said, "and I hope that this will help them (the WSSC) take heed and prevent such things in the future."

Other businessmen said that trying to take any legal action against the WSSC for losses would be "like running into a brick wall."