One of the largest undeveloped parcels of land in eastern Loudoun County, the 357-acre Claude Moore Conservation Education Center, was sold to a builder yesterday for $8.5 million by the National Wildlife Federation.

The developer, Miller and Smith, said in a statement that it is studying what to do with the land, located near Sterling in the fastest-growing area of the county, and will announce specific plans within 60 days.

The sale culminates several years of controversy over the historic farm, which Moore, a 94-year-old physician, donated to the wildlife federation in 1975 and on which he still lives. Federation officials rejected plans to sell it two years ago, partly because of Moore's strong opposition.

The sale could run into local opposition because Loudoun County's master plan calls for the parcel to remain undeveloped, although the land is zoned for one-acre house lots. Any proposed increase in the zoning density would require county approval.

The wildlife federation's board, meeting in Seattle, voted 25 to 3 Wednesday to sell the land, and papers were signed yesterday, according to federation spokesman Adrienne Jones. Moore, who attended the meeting, could not be reached for comment.

The Moore Center land, which has been open to the public for hiking and cross-country skiing, is located on Rte. 637, southwest of Rte. 7. Laced with 10 miles of trails through meadow, woodland and scrub, and alongside ponds and marshes, it is home to 185 species of bird.

The federation will use the profits from the sale to set up a national conservation fund for endangered plant and animal species, Jones said. The federation will continue to operate its Laurel Ridge Conservation Education Center on Leesburg Pike 10 miles away in Vienna, and thought it unnecessary to have two education centers so close together, she said. Jones will continue to live on the land after it is developed, she said.

Jay D. Hair, executive vice president of the federation, the nation's largest conservation group, said in a statement that Moore's gift of land "will make it possible for us to have an even greater impact to save endangered species from extinction . . . . In a very real sense, Dr. Moore can be proud of his major role in saving this nation's precious endangered species for future generations of Americans."

But Betty Tatum, the Loudoun County supervisor whose district includes the Moore land, said the sale "will disappoint an awful lot of people in Loudoun County," herself included. She described the land as "our little piece of country."

"It gives me some pain that the wildlife federation, which we had considered a leader in preserving land and wildlife, is just like everybody else, it seems," Tatum said. "They're interested in getting the money out of it."

"We're interested in getting the money out of it because the land . . . is not terrifically useful," Jones replied. "The money can be put to better use for our purposes. The conservation fund will allow us to help the wildlife that is one of our mandates to protect."

Jones said the federation placed no conditions on development of the property, which she described as "not a beautiful piece of land."

The activities of the new fund for endangered species have not been determined, Jones said, but may include research, a fellowship program for graduate students, conferences or a computer data base.

Miller and Smith, a major housing developer and builder whose main office is in McLean, established a commercial property division several years ago.