County officials are hailing the planned $16.1 million purchase of a conservation easement on a 41-acre property in McLean as a significant step in Fairfax's effort to preserve open space.

The county Board of Supervisors has been criticized by some residents who have opposed developments that the board generally has favored. Some board members said the announcement last week of the largest land expenditure in the county's history would help show their commitment to protecting green space.

"We have an opportunity here with one of the most historic properties in the county to make sure that we can preserve it in perpetuity in its current state," Board Chairman Gerald E. Connolly (D) said at a news conference.

He said national, regional and county parkland covers 9.2 percent of Fairfax County. "I've asked the Park Authority to set a goal of 10 percent. And that last 0.8 percent is going to be the hardest because we are bumping up against buildup in Fairfax County. Land is scarce, and when we can preserve it or acquire it, that's a really good thing."

The property is part of the Salona estate, owned by Daniel H. DuVal and Clive DuVal III, sons of the late state Sen. Clive DuVal II (D-Fairfax). The DuVals have agreed in principle to allow the Board of Supervisors and the Park Authority to acquire a conservation easement on the land, protecting it from development and allowing the Park Authority to create a park and preserve natural and cultural resources.

The DuVals would still own the land. With the easement, they would give the county the right to use it as a park. If the brothers decide to sell the land, the county would have the right of first refusal. The DuVals could sell the land for about $40 million, according to county officials; zoning regulations would permit more than 80 homes there.

The open space would include athletic fields, a playground and a picnic area. The county government still must find the money to pay for the easement, but officials said they were confident they could finance it, perhaps through a public-private partnership. The land is south of Route 123 (Dolley Madison Blvd.) along Kurtz Road and Buchanan Street.

Supervisor Joan M. DuBois (R-Dranesville), flanked by Connolly and other county officials, made the announcement at a news conference at the McLean Government Center. DuBois called the agreement "a very exciting opportunity for the McLean community. We have been able to preserve in perpetuity a very, very important historical piece of property," DuBois said.

Henry "Light-Horse Harry" Lee, a Revolutionary War hero and Virginia governor, lived at Salona. Historians believe that President James Madison and his wife, Dolley, sought shelter there while British troops were burning the White House during the War of 1812. During the Civil War, a Union Army headquarters was located there.

The agreement to purchase the easement has not been completed. DuBois has scheduled a meeting for Oct. 13 to allow members of the public to ask questions.

Kevin Fay, who represents the Dranesville district on the Park Authority board, said that given the unprecedented expense for the easement, "We want to feel comfortable that we have community support for this before we go forward."

Officials said an agreement would allow the Park Authority to build two rectangular athletic fields, a playground, a picnic area and a 100-space parking lot. An unpaved trail would fill in a gap in the Park Authority's system by linking it to the Pimmit Run Stream Valley. Most of the acreage would be preserved as managed woodlands.

The county also would have the right of first refusal to purchase the circa 1805 home on 7.8 additional acres at the center of the property. That land is protected by an earlier conservation easement that Daniel DuVal and his wife, Karen, established in 1971.

The DuVals would keep an additional three acres in the southwest part of the property near Wendy Lane and all rights to that land, including allowing it to be developed.

The Northern Virginia Conservation Trust, which worked with the DuVals for four years on the idea and first presented it to the county, would be "the enforcers of the conservation easement to make sure that the Park Authority and the county live up to the terms of that agreement," said Michael Kane, the Park Authority's director.

"Certainly, this property has tremendous benefits for the community and the county," Kane said. "This is really the preservation of one of the last, largest pieces of property in the McLean area."

The easement would guarantee "that there will be no residential development here at any point in the future. It's a historically significant property, and having access for cultural surveys and interpretive programs we feel is a tremendous benefit," he said.

Kane said the Park Authority and the county would put $3.15 million down, with the balance paid over a 20-year period plus interest.

Because the county does not have all the money for the easement available, Fay said it would require some creative financing. County voters approved a $65 million park bond last year, but Fay noted, "We only have a $12 million budget for land acquisition as part of that bond for the next four years. The price tag of [the easement] is significantly in excess of that."

The DuVals have shown "the ultimate in community spirit," Fay said. "They could have chosen the easy way out and sold their property for a much more substantial gain."

The public meeting will be from 7 to 9 p.m. Oct. 13 at the McLean Community Center, 1234 Ingleside Rd. For information, go to www.fairfaxcounty.gov/dranesville/current_topics_of_interest.htm.

Clive DuVal II and his wife, Susan, in their 18th-century house, Salona, in 1966. The house is not included in the planned conservation easement. The county wants to build athletic fields, a playground and a picnic area on 41 acres near the home.The Salona property in 1862. Henry "Light-Horse Harry" Lee, below, a Revolutionary War hero and Virginia governor, lived there. Historians believe that President James Madison and his wife, Dolley, below, sought shelter there while British troops burned the White House during the War of 1812.