CSX Minerals Inc. of Richmond, ending its battle to build a planned community on more than 1,600 acres of prime land in Loudoun County, has sold the tract for more than $26 million.

The land, known both as the Cameron Glen area and the western Pocahontas tract, was sold in two separate transactions.

Southmark Corp. of Dallas last week paid $18.1 million for 1,342 acres on the north side of the Leesburg Pike (Route 7), south of the Potomac River. Radnor/Loudoun Corp., a joint venture of Buchanan and Co. of Rockville and Radnor Corp. of Radnor, Pa., purchased 339 acres on the south side of the pike for an estimated $8.5 million. Radnor Corp. is a subsidiary of Sun Co. Inc., a Pennsylvania-based petroleum production and refining firm.

Charles Tremel, a Southmark executive, said Friday night that his company has not yet decided how it will develop the massive tract on the north side of the Leesburg Pike.

Robert Buchanan, president of the Buchanan and Co. of Rockville, said his company is designing an office park on the acreage to the south. The Loudoun County Board of Supervisors is expected to vote Oct. 15 on the developer's request for a blanket special exception to allow construction of offices on the parcel, currently zoned as a planned development industrial park site.

Both Tremel and Buchanan said their companies were attracted to the sites because of their proximity to the new Dulles Toll Road, the Washington/Dulles International Airport and the site of the state's Center for Innovative Technology, which will be built on Route 28 near the toll road intersection.

"Loudoun County, the Dulles Airport and the toll road area is great. There is a vibrance here that you don't often find," Tremel said.

Buchanan said he has "long been looking at eastern Loudoun with the knowledge that the Dulles road would ease traffic problems in the Route 7 area."

Southmark of Dallas is a land development and financial services company with investments across the United States, including a real estate division formerly owned by the Citizens and Southern Bank of Atlanta. Southmark Board Chairman Gene E. Phillips purchased that operation in the late 1970s.

Southmark controls $3.5 billion worth of real estate, including 30,000 apartments, 100 shopping centers, "a dozen or two hotels" and the Denver Merchandise Market, Tremel said. The firm also has major interests in a Houston savings and loan association and a West Coast insurance company.

CSX Minerals Inc. and Sunrise Development Co. of Cleveland had tried unsuccessfully to get Loudoun County officials to back construction on the north side of the Leesburg Pike of a planned community that would have included 3,845 homes, a neighborhood shopping center and offices. The Loudoun County Board of Supervisors rejected the proposal a year ago because of citizen opposition.

CSX Minerals is a subsidiary of CSX Corp., which also owns the Chesapeake & Ohio Railway Co. (Chessie System Railroads). The railroad system bought the Loudoun tract more than 20 years ago in hopes of building a power plant on the Potomac River. That effort also failed.

June Bechtell, head of economic development for Loudoun County, called the land sale "nifty." She said she is pleased by the Radnor/Buchanan alliance. "Buchanan has a good history of building. That is what we need. There is a need for doers," not just talkers in this area, Bechtell said.

Buchanan and Co. recently completed a 105-acre office development known as Parkway Trade Center near Herndon.

Buchanan said his company would widen the Leesburg Pike in front of its project and install traffic lights and double left-turn lanes if the project is approved. "We hope to create a monumental entrance to the complex with a landscape plan involving ponds," he said.