Since August, there has been a serious lack of rain along the East Coast. The flow of the Potomac River has fallen to historic lows. The Washington suburbs have imposed or are considering mandatory restrictions on outdoor water use.

But paradoxically there is no air of crisis in the offices of the Washington Aqueduct Division, a unit of the Army Corps of Engineers that supplies the District with Water. Officials at the aqueduct division say they aren't thinking about water restrictions.

It's not that the water officials are complacent, it's that the city, unlike the suburbs, does not rely on reservoirs for its water supply. It depends entirely on the Potomac River.

Reservoirs must be replenished in the winter in order to meet the heavy demand that comes with summer and fall. When rainfall is short in the fall and winter, the reservoirs drop and water managers call for restrictions on usage.

Since August, the Washington area has received 9.19 inches of rain -- less than half of the 19 inches considered normal for the period.

The widespread period of dryness has helped reduce the Potomac's flow in January to 1.3 billion gallons daily -- the normal flow is 10 billion gallons. However, the city's total demand on the river was only 330 million gallons daily, far below the amount of water available.

During February, the river's flow may increase to four billion gallons a day, according to National Weather Service forecaster Leo Harrison. The prediction is based on expected increases in rain in the Potomac River basin, which extends to West Virginia, western Maryland and Pennsylvania.

The city could experience a brief problem in late summer or early fall, aqueduct officials said, if total demand on the river were to exceed the river's flow for a couple of days. If that happened, with drawals from the Potomac by the District, suburban Maryland, and the Fairfax County Water Authority would be rationed under a staning agreement.

As a result, conservation now by the District would not be effective, Harry C. Ways, chief of the Army Corps of Engineers' aqueduct division, said. "It wouldn't do us any good to conserve now. The water would continue flowing by whether we used it or not."

For the future, the District's -- and the metropolitan area's -- long-term water outlook is said to be good.

Daniel P. Sheer, an engineer with the Interstate Commission on the Potomac River Basin, says, "The long-term problem (in the area) is solved."

Sheer bases his optimism on a computer analysis of reservoir storage, river flows and precipitation records and the impact of new water storage facilities in Maryland.

There are three main elements of the solution: Bloomington Dam on the North Branch of the Potomac, the proposed Little Seneca Lake in upper Montgomery County and the new intake on the Potomac being constructed by the Fairfax County Water Authority.

The three elements would work this way: When the Potomac's flow falls dangerously low, it would be bolstered with about 110 million gallons daily from Little Seneca Lake. If the low flow persisted -- a remote possibility -- beyond a few days, up to 300 million gallons would be released daily from Bloomington Dam.

Seneca, which could be ready by 1986, would provide a quick fix -- water released from the lake would reach the nearby Potomac in less than a day. Water released from Bloomington, which will be finished in mid-summer, would be harder to manage efficiently because it would take seven days to travel down the Potomac to the Washington area. If Bloomington's water would be released too soon, it would flow by the area before it could be used. The water could also be released too late.

The only potential hangup is a failure by city and suburban water officials to agree on a regional plan to pay for and then operate Little Seneca. There was a temporary falling out when Montgomery County wanted to make its sewage problems part of the negotiations, but it has dropped that demand and talks are moving forward.

Water and sewer rates in the Washington metropolitan area vary widely, with District residents paying the lowest charges for both.

Arlington residents also pay relatively low rates. The city and the country both draw their water from the Potomac River, the area's cheapest and most dependable source of water.

Some suburbanites are currently facing rate increases. Montgomery and Prince George's residents may have to pay 19 percent more for sewer service and 9 percent more for water -- an increase of about $29, from $183 to $212 a year.

In Alexandria, proposed rate increases would raise water and sewer costs from an average of about $173 to about $84. Fairfax County officials also are considering a boost in sewer rates.