The Potomac River, which provides the major source of drinking water for the Washington area, is flowing at less than one-third of its normal rate for this time of year.

Even before the pumping station fire yesterday that depleted water supplies in suburban Maryland, the river was so low that water officials said the Maryland suburbs could soon experience new water shortages unless several inches of rain fall in the next few weeks.

Although the National Weather Service's long-range forecast calls for "heavy precipitation," rainfall has been sparce since last November - down a total of 9.5 inches from normal.

"We are already at an alert stage," said Washington Suburban Sanitary Commission spokesman arthur Brigham. At the WSSC's Potomac station, where water is removed from the river for treatment and distribution to consumers, the water level yesterday was 157 feet above sea level.This is just a foot above the critical stage when the WSSC can impose mandatory water conservation measures on its customers.

"We've been watching it drop gradually by tenths of feet since late May," Brigham said. A month ago the level at the station was 157.5 feet.

The Maryland suburbs draw 80 per cent of their water directly from the Potomac River. The District which in turn serves Arlington and Falls Church, also gets its water from the Potomac. The Maryland suburbs would be affected first by any further lowering of the river's level because their intake pipes are higher than those in D.C., and thus more easily exposed by the lowering of the water level.

The last severe drought requiring emergency water conservation measures in the Washington area occured in 1966. The level of the Potomac, water officials said, is nearly as low now as then. The current flow is 1 billion gallons a day. At the end of June, the flow was 1.9 billion gallons a day, compared to the normal June flow of 4.2 billion gallons a day.

Residents of Fairfax County, Alexandria, and most of Prince William County get their water from the Occoquan Reservoir in southern Fairfax on the Prince William border. The level of water in the reservoir yesterday was described as adequate, and consumers in Northern Virginia were facing no immediate shortages.

Fairfax City, which has its own water supply, has circulated a standing voluntary request to users not to water lawns or wash cars. Arlington County and Falls Church have asked residents to conserve water on a voluntary basis.

The stifling temperatures of the past 10 days, which yestersay reached 100 degrees have exacerbated the potential water shortage. More water is consumed, especially for gardens and lawns during dry spells.

Scattered areas of the Metropolitan region draw water from wells and the ground water level is down 1.1 feet below the long term average for this time of year, according to the U.S. Geological Survey.

Water officials said they were concerned about the current low level of the Potomac because, historically, the river reaches even lower levels in August and September.

Already the prolonged dry spell has severely damaged the hay crop in the outer suburbs of Northern Virginia and the Shenandoah Valley and is threatened heavy damage to the corn drop. Farmers say they are dependent on those crops to feed dairy and beef cattle and will be forced either to buy grain and hay or reduce their herbs unless they get immediate rain.

Weather and agricultural officials say at least 4 inches of rainfall probably are necessary to maintain an adequate level of water in the river and prevent drought. The precipitation should occur in two or three days of steady rain.

The counties of Prince William, Fauduier, Warren, Culpeper, Orange, Goochland, Madison, Rockingham and Shenandoah have asked Virginia Gov. Mills E. Godwin to issue disaster area declarations so that their farmers can apply for low-interest U.S. loans and reduced freight rates for feed shipments.

"We are on the threshold of very severe damage," said Russell R. Tudor state extension agent in Fauquier County, which has 794 farms. "Rain would solve most of the problems but even with rain there would still be damage."

A Maryland agriculture officials said. "It's very spotty around the state. One place will get rain and the farm nevt to it won't. Hay is way off and the corn is at critical stage now. Pastures are way below normal."

"I'm not going to call it a drought yet," a Maryland official said, "But it's definitely dry and if we don't get a good, soaking rain in 10 days, we'll be in trouble."

One reason for the threatened water shortage in the area is the lack of extensive reserve here. For decades has urged that a network of dams be constructed to serve the region, but all, with the exception of the Bloomington Dan new under construction in Western Maryland, have failed to win approval.

"If some of the water from the heavy rain in March and April had been saved, we probably wouldn't have a problem in the next three four weeks," said Wayne Solley, and hydrologist with the U.S. Geological Survey.