The 3,200-acre Lorton prison property in southeastern Fairfax County would be turned into an expansive park and a residential neighborhood with up to 1,500 homes under a complex land deal with the federal government that will get its first public hearing Monday.

The plan for the Lorton site, one of the largest parcels of land open to development in the Washington region, would set aside more than 2,500 acres as open space or parkland, turning what has long been a federally owned prison complex for the District into a sanctuary for wildlife and a major recreation destination. The prison complex is scheduled to close in 2001, and the site, along the western edge of Interstate 95 just north of the Occoquan River, is viewed by many as a developer's dream.

Previous plans had called for massive development there, including as many as 10,000 homes and several multistory office buildings. The current plan, which some slow-growth critics still see as too intense, would limit development to a mix of approximately 1,000 single-family homes and town houses, a 450-unit complex for seniors, and small retail stores -- all on about 235 acres at the north end of the property.

"It's a major coup to be able to restrict the amount of development on this site in favor of protecting and preserving the environment," Fairfax Supervisor Gerald W. Hyland (D-Mount Vernon) said yesterday. "You would be hard pressed to find 3,000 acres like this located anywhere else in the region. It's a gem."

But Hyland's colleague on the 10-member Board of Supervisors, Elaine N. McConnell (R-Springfield), expressed disappointment with the plan, saying it needs more revenue-generating commercial development.

"There is no kind of economic area there," she said. "The county is in great need of revenue. I was hoping we'd get something more."

On Monday, the board will hear public comment. The proposal must be adopted as an amendment to the county's comprehensive land plan before it is submitted to the federal government.

Fairfax would need to come up with funds to purchase much of the 2,500 acres designated for parkland, and it could get hit with environmental cleanup costs as well, officials said.

Even if the county approves the plan, it will face many hurdles, chief among them working out the details of an unusual land swap.

The federal government, which owns the Lorton site, is willing to sell it to Fairfax but wants something besides money in return. The current plan envisions an exchange in which the federal government would trade its 235 developable acres at Lorton for a privately held tract on nearby Mason Neck.

Under that arrangement, made possible by congressional legislation last year, the trustees of about 800 acres on Mason Neck called Meadowood Farms would trade it for the smaller parcel at Lorton. William Lynch, a principal in the Meadowood Farms trust, would be permitted to develop the Lorton property.

Meanwhile, the Bureau of Land Management proposes to use the Mason Neck site, which is adjacent to a federal wildlife refuge, as a facility for about 50 wild horses and burros as part of its mandate to thin western herds by encouraging adoption of the animals.

"The federal government has no interest in a former prison site," said Rep. James P. Moran Jr. (D-Va.), who represents the Lorton area in Congress. "But it does have an interest in protecting its wildlife refuge on Mason Neck. There's better than a 50-50 chance that the swap will happen."

Lynch and the federal government are negotiating terms of the trade, but sources said they appear far apart. County officials say Lynch believes his land is worth $38 million, while federal officials set the amount at about $17 million. A recent county appraisal of the site came in at about $8 million.

"Value has been the major issue trying to make the swap work," Hyland said. "They are still trying to work the numbers."

Lynch did not return calls yesterday.

Assuming the land swap were to go through, the county would still need to come up with the money to purchase much of the 2,500 acres for parkland, to be operated by the county Park Authority. County officials estimate the price at anywhere from $1.6 million to $16 million. In addition, Moran said, the federal government is unlikely to pick up the tab for an environmental cleanup, which he said could be significant.

The cost to county taxpayers for acquiring and maintaining the property worries some.

Al Akers, a member of the citizen advisory committee that worked out the proposal, said he favors more development on the Lorton site -- up to 3,900 homes in addition to commercial properties -- to generate tax revenue to offset the cost of the parkland.

"My only concern is: Can Fairfax County afford to have the large portion be placed into open space?" Akers said. "Each of us who live here would love to have that, but can we afford that?"

Others have argued against any development, saying the property should be left in its natural state, even if that costs more.

"What I hear from people is the need to preserve as much open space as possible," said Supervisor Sharon S. Bulova (D-Braddock). "That's what I'm going to be rooting for."

County officials say acquisition of the Lorton site, which sprawls from the Occoquan River north to Pohick Road near Springfield, would be an enormous boost to Fairfax and especially to Lorton, an area thought by some to have been forgotten in the county's economic boom.

"This is the single most important item that has occurred in southern Fairfax," said Neal McBride, co-chairman of the citizen advisory committee. "This is an opportunity for Fairfax to plan something from the ground up. It's got a lot of good stuff."

McBride's group spent four months developing the site plan, which includes hiking and biking trails, a county-run golf course and sites for future schools. The project could take three to five years to develop.

The county landfill and trash incinerator are on the property, as is land set aside for an expansion of the county's water treatment plant on the Occoquan. Under the plan, most of that property would eventually become parkland, McBride said.

"It's really going to mean something for my grandchildren," he added. "They are the ones. If we do it right, we'll have some fine recreation opportunities and some nice homes they might buy someday."

The exact nature of those homes is unclear. The plan would limit the overall number of residences at 1,500, including some low-cost housing required by the county's affordable-dwelling ordinance and the 450-unit seniors complex, which would include a continuum of care -- independent living through nursing home.

If the land swap deal falls through, the maximum number of residences would be reduced to about 1,000, including the seniors facility.

On Mason Neck, the BLM project would be the first permanent facility on the East Coast for wild horses and burros. Hord Tipton, eastern director for BLM, said the site would provide a place for children and adults to learn about wild animals. "Public education is our prime objective," he said.