The strict water rationing measures imposed in suburban Maryland were almost completely rescinded yesterday 20 hours after they were first announced. Officials reported that widespread conservation efforts had eased the water shortage they had earlier described as critical.

Major businesses and offices around the area which were told to close were allowed to reopen at 5 p.m. yesterday as were swimming pools and other facilities using a lot of water.

Moderate conservation measures are still being urged the outside use of water is still banned except between 9 p.m. and midnight.

Washington Suburban Sanitary Commission General Manager Robert S. McGarry explained at the midday press conference that the 1.2 million residents of Montgomery and Prince Georges counties had restricted watee demand to 100 million gallons yesterday, down 70 millon gallons from Wednesday.

This conservation effort allowed the WSSC to build reserve storage capacity nearly to normal levels, McGarry said, alleviating the fear that heavy use of water reserves in the first hours of the crisis had left an insfficient supply to cope with fires of other emergencies.

The WSSC's Potomac water treatment plant, whose breakdown Wednesday morning triggered the shortage, is now working at about 75 per cent of normal capacity, although it is a patched-up system which will limp along until Thursday," according to Prince George's County Executive Winfield M. Kelly Jr. By then repairs at the plant are expected to be complete.

"The critical period will really continue until next Friday," said Montgomery County Executive James P. Gleason.

The abrupt about face by the WSSC came ass special teams of Prince George's County police were looking for violations of the emergency rules.

The midday decision also came after scores of businesses and office buildings had shut for the day in compliance with the order about which many had complained. M the Sears & Roebuck department store in White Oak, a skeleton staff scurried around to call 500 employes back into work.

"Personally - I can't speak for the store - I'm confused by [the sequences of events]. I don't understand it," said Sears official Milton Ayres.

Vera Berkman, chairman of the board of WSSC commissioners, defended both Thursday's decision to declare an emergency and yesterday's decision to decclare that it was over.

"We don't think we had an overreaction. It's better to be safe than sorry. What we did make good precautionary sense," she said.

WSSC officials made the original emergency declaration along with the two county executives, after they realized that on Wednesday, the first day of the emergency, demand for water had not been reduced and reserves were critically low.

As they made their declaration, however, water conservation efforts were apparently already proving effective. But they did not yet have that information.

The on-again, off-again nature of the emergency rationing measures merely added to the sense of confusion that had been building the last three days among people affected by it.

"We're so balled up here, we don't know when Cristmas is comingup," said a security guard at the IBM facility in Gaithersburg last night, after restrictions were relaxed.

Earlier in the day, Ed Russell, public relations officer for IBM, said, "I think our main problem is just the paucity of information as to waht was expected of us.

"On Thursday, we were thinking that mostof the crisis was over. When we heard the press conference . . . we were surprised by the crisis sound to it," he said. "After the press conference we were trying to figure out what would be the policy about closing."

Eventually, the twin IBM facilities in Gaithersburg and Bethesda closed and about 3,500 employees took the day off.

The same sense of chaos was evident at Montgomery Ward's department store at Iverson Mall in Hillerest Heights. Confused about whether the rationing ban applied to them, store executives spent all night trying to get an explanation from the WSSC.

In the morning, when none came, they left the Iverson Mall store open - only to be confronted by Prince George's County police, who ordered them to shut.They refused.

Then, just as WSSC crew, called in by police, got ready to turn off water to the store, relaxation of the emergency ban could legally open in three hours anyway, police and WSSC crews turned around and went away.

Some store officials said later they were perplexed by the decision to close some shopping malls, like Iverson, while in other shopping centers, identical Montgomery Ward stores, using identical amounts of water, were permitted to remain open.

When the order for certain businesses to close was announced, the WSSC said it would apply only to non-essential facilities which used more than 15,000 gallons of water daily.

Bill Austin, head of WSSC's customer servics department, explained that, at some malls, all individual stores' water usage is lumped together, pushing the whole mall above the 15,000-gallon cutoff mark. Elsewhere, stores in malls are billed individually.

Although Austin said that the WSSC had intended to spend Thursday night calling all the 160 or more businesses which would be required to close, left them helpless to do more than answer queries.

"I doubt if we could even have gotten an outside line," Austin said.

The confusion was spread to federal agencies too. All nonessential local state and federal facilities were to be closed under the order, but the WSSC left it up to individual agencies to decide if they were essential.

"We couldn't determine who was essential and who was not. Some of these operations are so classified they couldn't even tell me about it," he said.

At the same time as the businesses and government agencies were trying to figure out their roles in the crisis, WSSC officials took steps to prevent reporters from getting information from different sources within the agency.

By yesterday morning, reporters were barred from entering the potomac pumping plant on River Road, WSSC Information Director Arthur Brigham said this action was taken not because plant engineers were giving out information that contradicted the information being given out at headquarters, but for safety purposes.

He conceded, however, that there was a problem with engineers giving interviews, which resulted in the public getting contradictory information.

At the Potomac plant, three pumps were in operation yesterday pushing purified water into pipes that feed Montgomery, Prince George's and part of Howard counties, while another three were pulling raw water from the Potomac in to be purified.

This was an improvement over Thursday, when only four pumps could be used, in part because the plants electrical system, damaged by a small fire Wednesday, was operating at only half normal capacity.

The plant uses four electrical trnasformers, through which electricity flows into the system. Two were damaged in the fire, and these are expected to be replaced next week.

The emergency caused the WSSC to cut off the 1.3 million gallons of water it ususally sends daily to Howard County, and officials there have declared a water shortage, requesting a temporary halt to all outdoor uses of water.