Fairfax County officials and real estate consultants for Exxon Mobil have begun wrangling over the future of the company’s 118-acre campus in Merrifield, even though the property, which the energy giant plans to vacate, has not yet hit the market.

Irving, Tex.-based Exxon Mobil announced in the summer of 2012 that it would relocate its Fairfax County operations to Houston in early 2014. The decision is expected to move 2,100 jobs to a 385-acre office complex in Texas, part of a broader consolidation by the company.

The move will put one of Fairfax County’s most valuable properties on the market. The wooded 118-acre campus in Fairfax, located at the intersection of the Capital Beltway and Route 50, was owned by Mobil when the company was acquired by Exxon in 1999, and has been the headquarters of Exxon Mobil’s management of oil refinery, lubricant production, government relations and other operations.

In the spring, Exxon hired a real estate services firm Cassidy Turley to sell the campus. But for all the property’s attractiveness as a corporate headquarters, the task is not an easy one because it isn’t clear how much more a buyer might be permitted to build there.

As it stands, the Exxon campus, at 3225 Gallows Rd., has about 1.3 million square feet of office space. Its secluded location near the Beltway makes it a natural for a corporate campus or a security agency headquarters.

It has been discussed as a good fit for a future FBI headquarters, although Fairfax County officials would prefer to see the property sold to a private owner so it can remain on the tax rolls. Virginia Gov. Robert F. McDonnell (R) joined local officials in backing a location in Springfield for the agency instead.

Whoever buys it will also acquire the right to build between 400,000 and 500,000 additional square feet, according to the property’s current zoning approvals. A zoning change, however, could provide a buyer with millions of more square feet to build, potentially doubling — or more — the size of the campus.

Winning approval for future building would likely increase the property’s value and encourage development-minded buyers to ante up for it.

Some haggling over such a change has already begun. Representatives from Cassidy Turley met recently with Fairfax County Supervisor Linda Q. Smyth (D-Providence), whose district includes the Exxon campus.

Cassidy Turley representatives declined to comment on the discussions, or on their strategy for selling the campus, but Smyth said that they showed her a number of redevelopment scenarios, and she made it known to them that she is not likely to support the redevelopment of the campus into a much larger mixed-use center without major transportation upgrades.

Smyth pointed out that a number of other developments are already coming to the Merrifield area, including the mixed-use Mosaic District and multiple apartment projects adjacent to the Dunn Loring-Merrifield Metro station. “It’s a lovely site, but it doesn’t work for everything,” she said.

The road network, she said, wasn’t designed to handle any traffic beyond that.

“When we did the planning originally for Merrifield, we specifically looked at the transportation and began to think about what the capacity is for that road network, and whatever planned improvements for that road network that we could see,” Smyth said. “So our transportation network for the Merrifield area is pretty much maxed out.”

Smyth said she thought increasing the density on the site would require changing the area’s comprehensive plan, which constitutes extensive gathering of opinions from residents.

“That presents its own set of challenges. Once you open something up like that, be careful what you wish for. We would have to go through a community planning framework,” she said.