Four years after Aldie Mill was donated to the state of Virginia, bids are about to be sought for restoration of the interior of the historic Northern Virginia structure whose customers once included President James Monroe.

The mill, built in 1807 on what is now Rte. 50, 34 miles west of Alexandria, was once the largest flour mill of its kind in Loudoun County. It was the only mill in Virginia powered by twin overshot wheels, in which water flows over the top of the powering wheel. The five-story brick and fieldstone mill closed in 1971.

In 1981, the mill and its surrounding 3,000 acres were donated to the Virginia Outdoors Foundation by James Edward Douglass, whose family had operated it continuously for six generations.

An English millwright has begun restoring the water wheels and other machinery. Last year, the mill building itself was surrounded by steel shoring to prevent it from collapsing, and its floor was braced.

Proposals are due later this month from applicants who want to submit their qualifications to be the project's general contractor. The outdoors foundation will decide which applicants appear capable of doing the job, then invite them to submit bids. It is hoped the work can begin in the fall, said William J. Davis, the Richmond consulting engineer supervising the work.

The restoration will include the main mill building and two other buildings, one of them a smaller mill.

The work will aim for historical authenticity rather than technological perfection, Davis said. For the brick exterior, for example, he said, "we don't want a perfect surface. We want the charm and character that the years have produced." Only a few metal bolts here and there will inject the modern era into the 19th century building, Davis said.

The interior work could be done within about a year, but installation of the machinery will take a few more months, he said. After that, there will be some landscaping work, including installation of a parking lot.

The foundation anticipates no shortage of interested and qualified contractors, Davis said. "A lot of people want to do it for the honor of saying they've done it," Davis said.

The restoration is budgeted at $1.1 million, all to be raised from private donations. As of May 1, $682,564 had been collected, said Philip L. Chabot Jr., a board member of the Virginia Outdoors Foundation. "We're really pleased," he said.

The foundation board hopes to reopen the mill in 1987, and "the objective is basically to have it in an operating condition," Chabot said. He said the foundation hopes the mill will pay for itself through donations, admission fees and mill work.