Despite recent rains, experts are warning that the Washington area could face a water shortage this summer.

Drought is so severe in part of the Potomac River's basin that the odds have become five times greater that water restrictions will have to be imposed in the region by late summer. Ordinarily, the odds against any rationing would be more comfortable 25-1; they are now only 5-1.

A pessimistic outlook has just been produced by the National Weather Service and the water-supply cooperative comprising local water utilities, the U.S. Geological Survey and the U.S. Fish and Wildlife Service.

"I've never seen anything like it," said Daniel P. Sheer, director of the cooperative, describing drought conditions in the Shenandoah River basin, which supplies about 40 percent of the Potomac's flow during the normally dry late-summer months. "There is no moisture in the soil. It will take an extraordinary amount of rainfall to get any flow out of the Shenandoah this summer."

Sheer said that if summer rainfall is as light as it was in the drought year of 1966, outdoor water use would have to be banned for about 50 days and restrictions would have to be placed on indoor residential and business use for about nine days.

The Weather Service declines to make long-range forecasts. It will only say that the next 30 days should bring above-average rain for the immediate area. Gordon Barnes, weather forecaster for WDVM-TV and CBS News, does make long-range predictions, and he expects drought conditions through Labor Day in the area extending from Washington into the Shenandoah Valley.

"It doesn't look very good," Barnes said. "The drought will have serious impact."

Any water restrictions would presumably be tied to an agreement that strictly allocates Potomac water when the river's flow falls below 1 billion gallons daily. All the area's jurisdictions signed the agreement, but because most of Northern Virginia does not draw water from the Potomac, it is not clear if Alexandria, Fairfax County or Prince William County would be bound by any rationing.

However, the District and suburban Maryland are both heavy users of Potomac water, and they would have to make do with smaller shares during extremely low flows.

Sheer said the outlook could improve if the nearly completed Bloomington Dam's gates could be closed so water could be stored at that major impoundment in western Maryland. But that decision is up to the dam's builder, the Army Corps of Engineers. The corps says it doesn't yet know if it can close the gates in time to collect enough water to head off any water shortage this summer in the Washington area.