Right now we're praying for a flash flood." Janet Konopa, mother of 12, said after she learned that the water would be cut off tonight here and rationed for the indefinite future.

With 40 tp 50 loads of laundry a week, scores of dirty dishes after every meal, six daughters who insist on washing their hair daily. Konopa does not know how she is going to manage.

The Konopas are among the 1,000 residents of this peaceful Loudoun County community, 47 miles west of Washington, who, starting last night, face water rationing because of a season-long drought.

Today, as a light rain teased the town and its parched surroundings. Mayor Jeffrey Wolford met with National Guardsmen and telephoned surrounding communities seeking relief.

Round Hill's reservoir, fed by two mountain springs, one of which has been dry for weeks, is down from its usual 1-foot depth to an alarming four feet - barely enough to meet the town's needs for two more weeks - even with stringent conservation measures, said Wolford.

Townspeople have been warned to boil drinking water which has turned a cloudy gray. "It's the color of light beer," observed one startled citizen as he drew a glass. State health department officials say they are not sure the town's chlorination system is killing off the bacteria that may be suspended in the particulate matter discoloring the water.

The water will remain off through out the town for at least 12 hours a day, and will be on only during selected periods of the early morning, midafternoon and evening.

Throughout the town today, stoves, crowded with the traditional Thanksgiving fare of turkey, giblet gravy and yams, also featured large pots of boiling water.

We're drowning our sorrows with wine," remarked Mary Anne Graham, who prepared a Thanksgiving feast for four generations of family, but served no water.

"It's a catastrophe," said 92-year-old Pearl Graham, maltriarch of the gathering.

For the Konopas, the logistics of meeting the needs of 12 children ranging in age from 22 to 1, already limited to one bathroom and one sink, were staggering.

For starters, Janet Konopa, 42, said she is going to keep the bathtub filed with water so she can flush the toilets when the water is off. She said she will soon begin storing drinking water in jugs, milk bottles and thermoses for her thirsty brood.

As for laundry, she said she can not afford the $50- $60-a-week expense of taking it to a laundromat, so she will begin hiding her children's clothes instead, hoping to deter them from going through their clothes quickly.

"As for baths for 12 persons, it's going to be little tight," said Michael Konopa, 42.

"I'll check the kids and the cleanest ones get in first, the dirtiest, last," said his wife. "The biggest kid will come out the cleanest," she said, revising her plan.

Michael Konopa, a lithographer who like most of the town commutes to the Washington area, said he will not be able to wash at home in the morning.

"I'll take my razor and toothbrush to work in the morning," he said.

Meanwhile, Wolford will be looking at a number of possible solutions to Round Hill's water problems. Purcellville, three miles east of Round Hill, has offered the town 15,000 gallons of water a day, about one-third of Round Hill's needs.

In addition, Wolford said the National Guard may be willing to call in trucks from as far as Richmond to haul in outside water to the drought-stricken community.

Despite the light rain today, Wolford said it would take at least two heavy rains totaling four to five inches to replenish the town's 10-million-gallon water supply.