The wood turtle that ambles along Loudoun County waterways is a handsome enough creature, and not at all common in Virginia. But as rare animals go, the turtle has nothing on the Northwest's spotted owl, a threatened species that pitted preservationists against the logging industry this summer.

The white trout lily that brightens a few spots along the Potomac River each spring won't grab many headlines either.

But the lily, the turtle and a score more uncommon plants and animals have inspired Loudoun activists to propose that the county government spend $5 million to protect species that are rare in Virginia.

The county Board of Supervisors voted unanimously last week to let Loudoun's voters decide March 12 whether the county should sell bonds to buy unspecified "sensitive natural areas." State officials and the private Nature Conservancy say the referendum may be unprecedented in Virginia as a method of protecting special plant and animal habitats.

Leave it to Loudoun to be on the cutting edge of environmental activism. An occasionally fractious mixture of longtime farmers and affluent newcomers who fled the inner suburbs for "farmettes," Loudoun residents demonstrate a high level of pride in their scenic mountain ridges and other pastoral delights.

The county, one of the most rural in the area, lacks public transportation, and nearly half of its local roads are unpaved. But bumper stickers proclaiming that "Loudoun's beauty is everyone's duty" are ubiquitous. The fervor for the land has its practical limitations, however, and the March referendum is being described by some county activists as a test of the public's commitment to the environmental movement.

Though many residents say the environment is their top priority, the quality of the county school system and the real estate tax rate are of no small concern either.

The open-space referendum will be held amid deliberations on Loudoun's fiscal 1992 budget, and officials say the county is roughly 10 percent, or $30 million, short of its needs. Also on the March 12 ballot will be a $31.5 million bond issue to build a high school that some county officials say may be too expensive and include more athletic facilities than voters are prepared to support.

Loudoun's many environmental groups have become increasingly visible and vocal in planning and land use issues during the three years that the current Board of Supervisors has been in office. The movement may have reached a new level of activism with the filing of a citizen lawsuit in September challenging county approval of a major residential development near the rural town of Round Hill.

Peggy Maio, of the Piedmont Environmental Council, which is active throughout the rolling countryside of north-central Virginia, said Loudoun has generated "a huge increase in PEC membership in recent years."

Some developers, who asked not to be identified, said the environmental movement is made up of just a few dozen energetic activists who make it look bigger and stronger than it is to halt most growth.

All seats on the Board of Supervisors are up for grabs in November 1991, adding to the political tension next year. Some in Loudoun say a clash between the budget and land preservation may be inevitable.

"The conflict will arise if the referendum is not a one-shot deal," said William Mims, chairman of the Loudoun County Republican Committee, which has not taken a position on the open-space bond issue.

Referendum organizers and the county planning department say they would like to see a series of major land purchases over several years in which the county buys attractive or environmentally sensitive properties from willing landowners to save the land from development or other changes.

But "now is not a good time" to ask the voters to approve a habitat protection referendum in the $50 million range, said Miriam Westervelt, co-chairman of the Loudoun Open Space Advisory Committee.

Among the supporters of the open-space referendum is Wesley Parmer, a junior at Broad Run High School who built two eagle nests near the Potomac River for a Boy Scout project. A private proposal to build a golf course on that land "would doom the nests," he told the Board of Supervisors at a recent public hearing.

Officials and activists say no decision will be made for some time on which properties would be purchased if the March referendum passes.

At the suggestion of Loudoun activists, the state government's Natural Heritage Program is conducting a three-year survey of significant natural areas in Loudoun, geared toward protecting species rather than saving pretty views.

But the two goals "could mesh very nicely," said state ecologist Chris Clampitt.