Fairfax County will decide in the next few months whether to adopt strict controls on growth in what many have called the suburb's last frontier.

A citizen task force has recommended limiting construction in the county's western quadrant, one hundred square miles of farms and woods and large estates 30 miles west of Washington. At the same time, a separate and more prodevelopment panel has urged the board to approve intense commercial construction in one 5,000-acre area of the quadrant.

The undeveloped west, offering millions of dollars in potential profits, will serve as the final battleground in a war that Fairfax's powerful developers have waged for two decades against controls on growth. It offers what environmentalists see as the last chance to preserve some open space and protect the drinking supply of 600,000 Northern Virginians.

The battleground is the Occoquan watershed, a full quarter of Fairfax County that drains into the Occoquan River, which, in turn, provides drinking water for Alexandria and much of Fairfax and Prince William counties.

Little development has taken place there so far because there are no sewers, but the pressure to build will grow as Prince William, Loudoun and the rest of Fairfax become more congested, most officials agree.

Supervisors, who swear by the gospel of economic development as a way to reduce homeowners' taxes, say they are inclined to accept some version of the second panel's recommendations for major construction between Rte. 50 and Interstate 66, west of Fairfax City. The real fight on the board will come when the slow-growth advocates try to link the Rte. 50 and I-66 plan with stricter controls in the rest of the undeveloped west.

"If you are going to increase density in one part of the Occoquan watershed, you have to look at decreasing density in another," said Leslie Byrne, president of the Fairfax League of Women Voters. "We're very hopeful that the board will look at both together."

Decreasing density, however, means reducing options and so potential profit for landowners, and Virginia judges always have looked skeptically at any such threat to property rights. The supervisors have considered down-zoning several times before--most recently when they voted against it, 5 to 4, in 1978--but have always backed off or been slapped down by the courts.

"It's economic discrimination," said Suzanne Paciulli, who represented the Chamber of Commerce on the Occoquan Basin task force and strongly dissented from its conclusions. "The west of the county is the only place where there still could be affordable housing."

The task force recommended that most landowners in the watershed, who under current law could build one house on every acre, be permitted to build only one house on every five acres. Paciulli said the change would be unfair to people who have held their land for years as an investment. "There are no real developers down there," she said.

"That's the political question," said Byrne. "Does the county want to be in the business of guaranteeing risk-free land speculation?"

A separate task force on the Rte. 50-Interstate 66 area, working concurrently but not cooperatively, recommended an "urban village" of homes, stores and offices that could lead to more construction than now exists in Tysons Corner.

Board approval could be a boon to landowners, including influential lawyer and developer John T. (Til) Hazel, who with a partner holds 675 acres in the area valued at more than $2 million. Hazel served on the task force that recommended more development in the area.

"I see the board is going to do the thing west of 50 and 66 for Mr. Hazel no matter what," said Supervisor Audrey Moore, a longtime critic of Hazel. Moore said that if the board approves the plan for the Rte. 50-Interstate 66 area, which lies partly in the Occoquan watershed, it should at the same time act to protect other areas.

"On the one hand, you're giving landowners something and on the other you're taking something away, which is not politically popular," Moore said. "I think if the board does not agree to do both at the same time, it'll never happen."

Other supervisors said the two issues are not related. The 50-66 plan will attract jobs and high-quality, clean industry, they said, while the Occoquan plan could land the board in court. In addition, several supervisors said that the Occoquan task force had not convincingly shown that development is threatening the water supply.

"I don't think we need to cut out all development to protect the watershed," said Supervisor Joseph Alexander. "This 50-66 study has been a very thorough, expensive, expensive study. I don't see any reason to delay it."