Out in the western reaches of Fairfax County, where cornfields abut Pizza Huts in uneasy coexistence, a battle over drinking water is shaping up between a handful of irate homeowners and the county's thirsty water authority.

The residents of Chantilly Estates, a 30-home subdivision dating back to the early '50s, say the water authority is threatening their water supply by drilling into the same underground acquifer that about 20 homeowners tap for their water. As far as they are concerned, that's aqueous larceny.

"They're stealing our water," said Diana Widmer, one of the area's residents, who spent $5,000 to have a well dug and septic system installed two years ago.

A showdown in court was narrowly averted yesterday when the authority said it would postpone until next month five days of pumping from the aquifer that had been scheduled for this week. That saved residents from the uninviting prospect of carrying their water from hydrants during one of the summer's scorching weeks.

An aquifer is a layer of porous rock or sand containing water.

"I've got five adults at my place this week," said Edith Thompson, a Chantilly resident for 22 years. "What am I supposed to do when it hits 90, give them all sponge baths?"

Thompson and other homeowners traditionally have gotten their water from wells drilled in their backyards. They had to pay for the drilling and for septic tank systems. But they have avoided county water and sewage fees. When it comes to their independence, Virginians are as fiercely protective as Patrick Henry.

"The last thing I want is to have to hook up to county water with all that chlorine," said Widmer. "Right now, we're drinking right from the water table and it's sweet, clean and good."

So good, in fact, that the water authority - faced with an almost insatiable demand from new development in the metropolitan area's fastest growing county - decided to tap in.

After the severe drought of 1977, the authority hired a consultant who suggested drilling at three sites for underground water to supplement its reservoirs.One of the three: just across Route 50 from Chantilly Estates.

"This well could potentially provide us with a million gallons a day," said water authority spokesman James A. Warfield Jr. "That's as much as all 20 wells we have going right now combined."

The authority started drilling rather quietly in late June - about the same time that a number of residents noticed that their well water was becoming cloudy.

"I had no idea what was going on," recalled Frank Thorpe. "Then my next-door neighbor came over to borrow water because hers was so bad. I started checking around and that's when I found out about the drilling."

The situation got worse about two weeks ago when the county began pumping water from the aquifer. Water levels dropped to the point where some households had to do without water for a day or two.

Anticipating similar problems when it planned to pump again this week, the authority notified residents by mail last Friday to turn off their water pumps for five days. It said water authority employes would staff three area hydrants to help carry water to homes during that period.

That prompted an angry gathering at the Widmers' yesterday where residents plotted strategy. One resident brought Annandale attorney James De Deo, to the meeting. De Deo suggested that residents file suit today in circuit court to temporarily block the pumping.

The lawsuit proved unnecessary. By the end of the day, Warfield and other water authority officials said the pumping would be suspended until Sept. 15 when they expect that cooler weather will make five waterless days easier for residents to cope with.

But while temperatures may cool, temperaments most likely will not.

"They have no right to run us dry," said Widmer. "But knowing Fairfax County, they'll do just whatever they want to do."