Monday after Monday, year after year, William H. Hansbarger comes before the Fairfax County Board of Supervisors to plead his cases, his hands tucked in the pockets of his dapper suit, his measured voice always courtly and controlled.

Hansbarger is one of the best-known and most enduring zoning lawyers in a county where zoning lawyers form a special fraternity. As often as not, when he strolls to the podium of the Massey Building board room, Hansbarger is seeking approval for another McDonald's restaurant or another drive-in window, aiding a client who would make any lawyer happy in a fast-growing suburb like Fairfax.

But Hansbarger has tangled with the board on weightier issues than Big Macs. When the county made its first clumsy attempt 26 years ago to slow growth--and to take the decision of where growth should proceed away from the developers--Hansbarger was there, helping kill the measure in court.

Now, after decades of mixed success in channeling growth, Fairfax is trying again, and again Hansbarger is there, gently and with extreme politeness telling the supervisors they don't stand a chance in court.

The board is proposing a limit on development in the last sparsely developed expanse of the county, the 100-square-mile Occoquan Reservoir basin, by allowing only one house on every five acres in much of the wooded valley. The purpose, according to county staff, is to protect the quality of drinking water in the reservoir that serves 600,000 people in Alexandria and Fairfax and Prince William counties.

The plan has raised two fundamental questions that have been woven into the slow-growth debates since the 1950s: (1) Do property owners have a right to develop their land as they see fit? (2) Do limitations on development in fact work to exclude poor people?

Hansbarger addressed the first question last week at a public hearing on the Occoquan plan. "What zoning was really intended to do was keep the pigsty out of the kitchen," Hansbarger lectured the board. "You are going beyond the scope of what zoning is intended to do."

Hansbarger said he agreed that keeping the reservoir pollution-free is an admirable goal and a legitimate one for government to pursue. But he said that the 600,000 people who benefit from clean water should have to pay the price.

A zoning change from one-acre to five-acre lots, Hansbarger said, could reduce land to one-fourth its current value. The county plan would put that cost on the landowners, including several of Hansbarger's clients. "In my opinion, that is not a fair apportionment of the burden of protecting the water supply," he said.

The supervisors, who are likely to approve the Occoquan plan by unanimous vote, according to board chairman John F. Herrity, were not convinced. "What is their inherent right to go and destroy property that belongs to somebody else, like the Occoquan Reservoir?" Supervisor Martha V. Pennino asked.

Leslie Byrne, president of the Fairfax area League of Women Voters, said Hansbarger's argument implies that landowners should be guaranteed a profit on their investment. "With all speculation, there's an element of risk," Byrne said. "Those people who bought municipal bonds 20 years ago at 5 percent and took a bath weren't guaranteed a profit. . . . There seems to be an unwritten law in Fairfax that landowners should be different."

Byrne also rejects the notion that the Occoquan plan will keep poor or moderate-income families out of Fairfax by requiring that new homes be built on large, expensive lots. "We've had 25 years of this argument, and we don't have many poor people to show for it," she said.

When Fairfax passed a law in 1956 broadly requiring two-acre lots in the west of the county--the Freehill amendment that Hansbarger helped overturn--the Virginia Supreme Court objected in part because the law would "prevent people in the low-income bracket from living in the western area." Today, Fairfax County's population of more than 600,000 has an average household income of more than $34,000 and an average new home costs about $100,000. "Unfortunately, you're talking about very expensive homes, whether it's one acre or five acres," said supervisor Audrey Moore of Annandale. "There aren't many people who can afford to build a home on one acre of land in Fairfax County anymore."

Both questions on the Occoquan will likely be answered ultimately in the courts, where the county has rarely fared well in the past. Herrity says the county may win some cases and lose others on the Occoquan, but will not face the string of defeats that Hansbarger and other zoning lawyers helped engineer in the past.

"I think the board is in better shape to deal with the courts now," he said, recalling with distaste the early 1970s when he often cast the only dissenting vote on a fervently slow-growth board. "The whole atmosphere is different."