Under a newly approved plan long advocated by outdoors enthusiasts, Fairfax County is moving ahead with a project to create a cross-county trail stretching more than 31 miles from Great Falls to Lorton.

In its meeting last week, the Board of Supervisors agreed to spend $100,000 on the first five phases of the project, which will link existing trails through land acquisitions and the construction of connecting paths and stream-crossings.

The resulting network of asphalt, crushed gravel and dirt trails would connect three major greenways--Difficult Run, Accotink Creek and Pohick Creek--and wind through parts of all nine of the county's magisterial districts. Eventually, after the county acquires the Lorton Correctional Complex property from the federal government, the trail would extend south to the Occoquan River and span 36 miles.

With "all the bells and whistles," including uniform surfacing of about a third of the trail with crushed gravel known as stone dust, the entire project could cost as much as $3.4 million and take several years to complete, said Supervisor Gerald E. Connolly (D-Providence), who has long championed the trail. A more modest approach that leaves the new segments and some existing ones as dirt trails would cost about $2 million and take up to 18 months.

Either way, Connolly said, "that's a pretty good bargain to get a 36-mile cross-county trail. This could be a wonderful legacy for future generations in Fairfax County."

Connolly and other advocates dismiss arguments over what sort of surfaces and other components the trail should have, saying the important thing now is to acquire the needed land and link up the existing segments.

"We should not let the perfect be the enemy of the good," he said. "We should move as swiftly as we can to complete the land acquisitions and the mileage markers and the signage. Once we have a trail that's all of one piece, then we can go back in subsequent years and perfect it."

Besides, Connolly said, land isn't getting any cheaper.

Bill Niedringhaus, president of a civic group called Fairfax Trails and Streams, said he expects the completed trail to be used mainly by hikers, although people could also travel the length of it on mountain bikes or horseback. About a third of the trail's existing segments are asphalt and thus suitable for road bicycles and rollerblades as well.

"This is pretty much the only possible route for a cross-county trail, because Fairfax County is so built up," he said. "It's important we act quickly before some of the last remaining pieces are sold and developed."

Of the 31.5-mile length of the initially planned route from Great Falls to Alban Road, existing trails account for 26.7 miles. Trails that still need to be built, totaling 4.8 miles, include three segments funded by a $1.2 million Fairfax County Park Authority bond program. An additional sum, ranging from $800,000 to $2.2 million, depending on the trail surface, is needed to finance the remaining segments. The $100,000 allocated by the board last week represents a down payment on that funding.

To complete the trail, Fairfax County needs to acquire about 10 properties worth an estimated $200,000. About $500,000 is needed for construction of 10 culverts and eight fair-weather stream crossings.

For the most part, the trail would wind through parkland and along stream beds. Among other links, it would connect Reston with Fairfax City.

"Almost the entire route is in the woods," Niedringhaus said. Signs are needed because "a lot of this area is really remote, and it's easy to get lost," he said. "There's a lot of little trails."

The widest part of the trail route is in the Difficult Run area in the north, said Niedringhaus, whose group has offered to help maintain the natural surfaces. Trekkers can see various types of wildlife along the route, including more than 50 kinds of birds. "There were even reports of a bear being sighted near Great Falls," he said.

Connolly hopes the trail will give Fairfax County residents a nearby alternative to hiking in the mountains to the west. It also would help preserve open space in an increasingly built-up part of Northern Virginia, he said.

And for businesses interested in moving to the county, Connolly said, the trail would be "yet another attraction in terms of having a livable community."