The continual rain that has soaked the Washington area since May has also washed away the threat of a serious drought for the first time since 1979, weather forecasters said.

What this will mean for area residents is an end, at least until winter, of threats of water rationing and emergency water-sharing among local water utilities. Contrasts in the water situation are sharp in areas such as Fairfax County where the Occoquan Reservoir now has water spilling over the top of the dam. For parts of last year it was unlawful to use water in Fairfax for anything but showers, toilets, cooking and drinking.

Within the District of Columbia and suburban Maryland for the last three years, residents have been urged to cut back on water use under threat of 50-day outdoor water bans and emergency rationing. But this year, D.C and Maryland water officials said, there will be enough water in the Potomac to keep lawns green, cars clean and swimming pools filled to the brim this summer.

Often, effects of a drought on the water supply are not readily apparent to residents who see water in the Potomac and reservoirs. But it has been a constant worry of area water planners in the last three years who feared a water crisis if demand on a dangerously low Potomac coincided with peak water demands. Until this year's wet spell, water planners also have been concerned that there would not be enough water pressure to fight a major fire.

This year, however, all worries about drought emergencies were erased when recent rains provided enough water to fill ponds, streams, reservoirs and the Potomac at well-above-average levels. The supply is expected to withstand everything except near-desert conditions for the summer.

And the National Weather Service hardly is predicting a prolonged dry spell. For at least the next 30 days it is forecasting well-above-average precipitation, continuing a rainfall catch-up that started in late February and has moved the Washington area from being short 8.22 inches of rain to a surplus of nearly five inches.

"Things look really, really good for the area's water supply," said Marjorie Johnson of the Washington Suburban Sanitary Commission. "We've even had to open two of our floodgates on the Patuxent River to allow for the runoff from all the rains."

James Warfield, a spokesman for the Fairfax County Water Authority, said "So far this summer it has been so wet that the only thing we have to worry about would be a drought as equally severe as the worst one ever that dried up the area in the 1930s. Now it would take a long string of dry months to really cause a water supply problem."

The below-average rainfall that touched off the nearly three-year drought began in late 1979, when only 29.32 inches of rain fell, and last year, when only 30.67 inches fell. So far this year 21.39 inches of rain has fallen, well above the typical 16.58 inches. The last time Washington experienced this much wetness was four years ago when an unusual winter storm spread a snow blanket over the area in January and February and tropical storm David hit in September and October.

"A drought like the one we've just been through seems to only happen every 10 or so years," said Frank Rosenstein, a fore-caster with the National Weather Service.

Soil moisture for crops, according to Department of Agriculture meteorologists, has improved so much that crops are now expected to be able to withstand short periods of drought.

About the only thing the heavy rains have not replenished is the area's water table. According to the U.S. Geological Survey, the underground water table that supplies water to wells has not been able to recoup its drought losses because the rains have been too intense and too short to filter to the water table. The Geological Survey, however, does not foresee any problems with area wells because of the low water table.

The 3 million people who live in the Washington area draw their water from three different and independent water systems.

The largest, serving half the area's water users, is the Washington Aqueduct, which provides water to all of the District of Columbia, Arlington and Falls Church. The aqueduct system is almost totally dependent on the flow of the Potomac for its water.

Montgomery and Prince George's counties are served by the Washington Suburban Sanitary Commission, which also relies on the Potomac for nearly half its water.

The rest comes from two small reservoirs on the Patuxent.

Although the reservoir for the Fairfax County Water Authority--serving Fairfax County, Alexandria and Prince William County--has good storage capacity, it also faces problems during extended dry spells because demand often exceeds capacity.

Water experts agree that the Bloomington Dam on the upper Potomac has helped, but not solved, Washington's water supply problems since it opened in 1980. Although this year's rain averted a crisis, hydrologists say dry weather next year could begin water problems for the area all over again.