Strict water rationing measures were imposed in suburban Maryland yesterday after earlier efforts to persuade Prince George's and Montgomery County residents to conserve water failed to relieve a critical water shortage.

In the first 24 hours after the breakdown of a key Potomac water pumping station Wednesday, residents used about the same amount of water as usual despite official pleas of conservation. The heavy demand hampered efforts to build up the water reserves that declined drastically during the first day of the crisis, although frantic repair efforts restored the pumping station to partial use yesterday.

Under the mandatory rationing program, all outdoor water use is forbidden and all swimming pools have been ordered closed. More than 160 businesses, office complexes and shopping malls have also been shut down along with all nonessential government officers.

Police in both counties have been authorized by county executives to issue citations to persons or businesses violating the emergency rules. Violation is a misdemeanor, punishable by a fine of up to $1,000 and six months in jail.

"This is not a game we are playing." Montgomery County Executive James P. Gleason told a press conference at the headquarters of the Washington Suburban Sanitary Commission. "These measures are absolutely essential for the safety of our people."

In addition to the mandatory conservation measures. WSSC general manager Robert S. McGarry asked all residents of both countries to cut their personal use down from the average 70 gallons to about 45 gallons a day by showering and flushing the toilet only once a day, and using a minimum amount of water for drinking and cooking.

Officials said that no large areas of Prince George's or Montgomery Counties were deprived entirely of water yesterday, as some were Wednesday. In fact, many resident's found a strong flow of water still gushing from their taps, which contributed to widespread skepticism about claims of a severe shortage.

But the authorities said near normal water service could be restored - and necessary storage tanks refilled - by midnight Saturday only if everyone cut back on their water consumption.

Although homes in parts of northern Montgomery County communities such as Olney. Germantown and Gaithersburg ran out of water entirely Wednesday, many people whose taps were still running expressed indifference to the problem yesterday or disbelief in its seriousness.

"We're waiting for someone to come in and tell us we have to close," said an employee of Harpair hair cutters in Gaithersburg, one of the areas where some taps run dry Wednesday.

"I can understand why people who can't do dishes or laundry getting upset about us being open, but if restaurants can stay open, I don't see why we shouldn't, the employe said yesterday.

There were some conservation efforts noticeable in the affected areas, however. "Look at me, you can tell I haven't been using any water," said Garry Ritter, a chemist with the National Bureau of Standards who took care to stay five feet away from the reporter questioning him. "I'd love a shower," he said.

The management of Montgomery Village in Gaithersburg shut off the water-cooled air conditioning system for 2,000 of their apartments Wednesday afternoon, but turned it back on yesterday morning after complaints from residents.

Meanwhile, at the damaged pumping station just off River Road in Potomac, engineers were urging a constant battle with the elaborate pumping machinery and the electrical system which powers it. At first, the problem was to repair pumping facilities damaged by the 21-minute fire Wednesday morning.

By yesterday morning two of the pumps that take the purified water from the plant and feed it into the 3,400 miles of pipe around the two countries were operating as were two of the pumps that pull raw water from the Potomac to feed it into the plant's cleansing system.

Having accomplished that, the engineers were trying to work a delicate balancing act, making sure the pulling power of the raw water pumps matched the output of the "finished water" pumps to prevent further malfunctions in the system, and to avoid drawing down water reserves at the facility.

Their task was complicated by the low level of the Potomac, which yesterday hovered barely above 157 feet above sea level, the minimum level at which the plant can take in water efficiently.

"I have a hunch we will live with this water shortage problem for a while," said Richard Hocevar, director of maintenance and operations at the Potomac plant, which normally pumps about 130 million gallons a day.

Hocevar said that he was considering using a makeshift damming system, which involves dropping baskets filled with rocks into the river just below the intake valves, to raise the water level.

In addition, Hocevar was wrestling with the problem of keeping part of the damaged electrical system in operation, while not making the two working transformers do the work that four transformers normally do when the plant is operating property.

Senior plant engineer Dale Hughes was concerned that these two transformers would become overloaded if too much power was demanded by the system, further complicating the attempts to balance the flow of water in and out of the plant.

In the midst of all this, a small thunderstorm near the plant shut power off completely about 3 p.m. yesterday causing a 10-minute breakdowns, But as soon as the storm passed, power was restored and operations continued.

The Wednesday morning fire did major damage to three key areas to the plant: a large "finished water" pump. numbered M-2 in the plant's numbering system, two of the four electrical transformers, through which power flows into the system, and the spage-page electrical control panel.

The damage was so extensive that repairs may go on for weeks, particularly since the machinery involved is unique to that plant's system.

Plant engineer Ernest W. Bond predicted that the replacement transformers could be ready in 10 days or so, but another WSSC official said it could take months to replace the intricate wiring of the damaged section of the control panel.

"We have to get right back to basics. It's like putting together a puzzle," said Tom Seck, the WSSC's assistant electrical supervisor for Montgomery County.

"(The fire) left everything in one blob." he added, estimating that there are more than 110,000 wires that must be replaced.

During the first hours of the crisis Wednesday, the WSSC's other major pumping station on the Patuxent River speeded up operations to provide a total of 77 million gallons of water to the area, which normally uses between 160 million and 170 million gallons daily.

About 27 million of these gallons came out of the Patuxent station's own reserves, which contained only about four million gallons yesterday morning.

Elsewhere, reservers from the 50 reservoirs, standpipes and holding tanks in the area were drawn down by a total of 60 million gallons with some, like the tank on Shady Grove Road and the resevoir in Wheaton, being down to nothing or almost nothing.

Even though some water was restored to all those holding areas when pumping haltingly began at 11:40 p.m. Wednesday, local officials still fear that low reserves pose a grave danger if any fires spring up.

At yesterday's press confernece, Prince George's County Executives Winfield M. Kelly Jr. emphasized the danger of fires.

To aid the suburban Maryland area in its problem, the District of Columbia Water Resources Department yesterday pumped about 15 million gallons of water into seven different areas in the two countries, using fire pumper trucks as conduits between District and Maryland hydrants in some locations.

The total breakdown was considered unusual by water experts in the area. "There are lots of backup systems there." said Cameron Wiegand of the Metropolitan Washington Council of Governments.

"What happened was unusual. You can't back everything up and that control panel is a hard thing to back up."

Wiegand also explained that, because the few interconnections between the water systems of the District, Maryland and Virginia, are made with extremely narrow pipes, there is not much one jurisdiction can do to help out another in times of crisis.

Jean Levesque, manager of the District's Water Resources, said yesterday that the 15 million gallons sent to Montgomery County to alleviate the shortage represented about 10 per cent of the District's average daily usage.

The WSSC would be billed for the estimated $7,900 cost of the water, he added.

Around the affected areas, residents expressed widespread ignorance about the exact nature of the problem, even though many showed a willingness to conserve.

Shirley Bower sat on the steps in front of her Montgomery Village apartment in Gaithersburg and watched her three children play as she said. "I think the problem is in the pumps, isn't it? All I understand is that I get my bill."

Another Montgomery Village resident, Janis Rayca, expressed resignation about the whole situation. "We're surviving," she said. "Last night . . . the four of us washed in one basin full of water.

"I'm relying on the 48-hours we heard about on the news. If this lasts any longer than that, I may go to my parents in Glen Burnie to do the laundry."