Hoping to stem the loss of trees and open space to development, a Fairfax County supervisor yesterday proposed creating a public preservation trust from donations by property owners.

The trust, which would be the first of its kind in the region, would be used to purchase undeveloped sites that would then be set aside for recreation or as nature parks.

"It is imperative that we explore options for funding that will allow us to acquire and maintain land for use and enjoyment today and for future generations," said Supervisor Stuart Mendelsohn (R-Dranesville).

Mendelsohn made his proposal as the Board of Supervisors also was considering whether to allow a multi-field sports complex on 117 acres near Centreville. After a four-hour public hearing, the supervisors deferred action until Jan. 24.

Known to supporters as the "Field of Dreams," the $20 million complex would have fields for baseball, soccer and football, as well as indoor and outdoor basketball courts. The Southwestern Youth Association sports league would pay for the project. Neighborhood opponents of the complex say it would increase traffic congestion, noise and lighting problems in their community.

But Southwestern, which has 16,000 children in its sports program, argued that the complex is needed to make up for a dearth of athletic fields in the rapidly growing Centreville area.

Attempting a compromise, the youth group recently agreed to eliminate an outdoor amphitheater from its plan, cut back on parking and limit the number of fields using lights at one time.

The public hearing on the complex ended the first meeting of the newly constituted board, whose returning members welcomed newcomer Catherine M. Hudgins, the county's first African American supervisor, and bid farewell to County Executive Robert J. O'Neill Jr.

Hudgins, a Democrat, defeated two-term Hunter Mill representative Robert B. Dix Jr. (R) in November. O'Neill, who departs Friday to head a government think thank, is being replaced by Anthony H. Griffin, currently deputy county executive.

Meanwhile, park officials told the board yesterday they are set to begin work on a cross-county trail system that would link existing trails to form a 35-mile path between Great Falls and Lorton. The initial phase is expected to cost about $100,000.

Under Mendelsohn's open-space preservation proposal, real estate owners could indicate a desire to donate by checking a box on their property tax bills. To encourage donations, Mendelsohn asked that the funds be used for projects near the donors' residences.

Fairfax lost 25,000 acres of trees between 1980 and 1990, Mendelsohn said, and is expected to lose 8,000 more by 2020. Without discussion, supervisors unanimously agreed to have county staff members study his idea.