One of the most valuable pieces of real estate in Loudoun County is a triangle of undeveloped land along the south side of the Dulles Greenway, bounded roughly by the Greenway, Old Ryan Road and the Loudoun County Parkway. The nondescript parcel — formerly not-very-good farmland — is desirable solely because of its location next to the future site of Ashburn Station, the western terminus of Metro’s Silver Line.

Last month, representatives of the property’s owner — the Claude Moore Charitable Foundation — gave regional business leaders a glimpse of their vision for a possible trail- and transit-based urban community on the site.

The Fairfax-based nonprofit group is quietly playing an active role in shaping plans for development on the 300-acre property. The foundation intends to sell off the land in parcels of 20 acres or more, attaching conditions that ensure that anything built there enhances the development as a whole, the officials said.

To maintain its nonprofit status with the Internal Revenue Service, the foundation cannot develop or actively market the property, trustee Guy M. Gravett said April 19 in a presentation to the economic development committee of the Dulles Regional Chamber of Commerce.

“We are allowed to . . . give people a vision of what we want,” Gravett said, “but we’re not going to be the one [doing the] building.”

The group’s deputy executive director of operations, Randolph Sutliff, said that the foundation’s main long-term goal “is to convert really bad farm ground into very valuable parcels for sale or long-term lease.” Funds will go to the foundation.

In promoting an urban, walkable development that includes green space and trails, the foundation is adhering to the vision of Claude Moore, Sutliff said, characterizing the nonprofit group’s founder as “a capitalist and a conservationist.”

Moore, a radiologist who amassed a fortune by investing in large tracts in Northern Virginia, formed the charitable foundation in 1987. The non-profit organization provides grant funding for educational and leadership programs for young people.

Moore bought the land, which had been known as Moorefield Station (the foundation now prefers “Moorefield”) before World War II, Sutliff said. When Moore died in 1991, the property consisted of about 1,200 acres of undeveloped farmland. The foundation later acquired about 300 more acres and waited for the land’s value to increase.

The foundation sold 900 acres in 1999 for about $58 million, Gravett said. After rezoning the remaining property, the nonprofit group sold 94 acres in 2005 for about the same sum it had received six years earlier for the much larger parcel, he said.

The group has continued its strategy of selling the land farthest from the future Metro station, while preserving the land in the center.

“We’re working on the edges of this property and holding the very best for last,” Gravett said. The foundation is moving slowly to maintain flexibility, mindful that the Silver Line is scheduled to arrive in 2020, he said.

“You want to make sure that when you’re at 2020, you’ve got enough real estate to make it worth the developer’s while,” Gravett said.

In the 25 years since Moore’s death, “the Greenway happened and Metro’s happening,” Sutliff said. “But more importantly, the Internet happened, which changed everything. It changed how people work, how people shop.”

Those changes have influenced trends in both commercial and residential development, Gravett said, and shaped the foundation’s vision of Moorefield. The group hopes to see an urban, walkable community with a mix of residential, retail, entertainment and office space.

“Nobody wants an office park,” Gravett said. “They want an urban environment.”