The 26th annual Morven Park Steeplechase Races will be held Saturday, perhaps for the last time under the direction of the foundation that oversees the historic mansion and its museums.

Trustees of the 1,050-acre Leesburg estate are negotiating with the United States Eventing Association to take over operations of the 38-year-old Morven Park International Equestrian Center.

Officials of the association, which is based in Leesburg, are conducting a feasibility study of the property and will present a business plan to their board of governors before the end of the year. If all goes well, they could sign a lease by Jan. 1.

The association, which is housed on land donated by Morven Park, has a relationship with the historic estate dating back to the 1960s, when it established an institute for training instructors that later became the equestrian center.

The school closed in 1991, but the equine events on the grounds have continued, including the spring horse trials, a three-day show in the fall and the Morven Park Steeplechase Races.

Jo Whitehouse, president of USEA, said her vision of the center goes beyond hosting the traditional events.

"As Loudoun County is being developed more and more, it's getting hard to find a place to ride a horse," Whitehouse said. She said that if the association takes over management of the center, she hopes to keep "beautiful open space available to the local equestrians as well as the local community."

A multimillion-dollar restoration of the Morven Park mansion, which has been home to two governors, began to strain the $40 million endowment of the Westmoreland Davis Memorial Foundation, and trustees began looking for someone else to run the equestrian center.

"Over the years, the value of the endowment has grown, but the number of activities and buildings that we've asked it to support has grown, and we are in a position to concentrate on what's most important and that's the preservation," said Will O'Keefe, the foundation's executive director.

Proceeds from Saturday's steeplechase, which is expected to draw as many as 10,000 people, will go toward the mansion's restoration.

Operating the center, which costs the foundation $100,000 to $200,000 a year, will require an upfront investment from the new lessee, Whitehouse said, because there is a backlog of repairs, including a half-refurbished barn and erosion near one of the arenas. She said the eventing association, a nonprofit organization with an annual budget of $2.4 million, would have to raise funds to underwrite such costs.

USEA, which has 14,000 members, also plans to move its headquarters to Morven Park and centralize its training facilities there.

The association was formed in 1959 to promote and educate people about eventing -- equestrian's triathlon, which involves dressage, cross-country and show jumping -- when competitive riding was evolving from a military-trained sport to a civilian one. Since then, the group has trained officials and instructors to set up and operate courses across the country.

Morven Park does not plan to offer many of its trail rides, dressage shows or hunter shows in 2006. Events not organized by the center, such as the Potomac Celtic Festival and the antique shows, will not be affected.

Whitehouse said that if the association takes over the lease, she hopes to open the facility to many other equestrian and non-equestrian activities.