More than 4.5 million square feet of office space is being proposed for construction at the interchange of Hunter Mill Road and the Dulles toll road.

The square footage is almost equal to a third of the total commercial space planned in the entire Fairfax Center area, according to the Fairfax County planning staff.

The Hunter Mill Road interchange is the first exit from the toll road west of the Leesburg Pike-Tysons Corner exit.

The proposed office developments have propelled Fairfax County residents, politicians and a handful of lawyers and developers into a bitter battle over the future of more than 300 acres on three corners of the interchange. Developers say the most logical use of the land is commercial and point to the Park Ridge Office Park now under construction on the southwest corner of the interchange as a precedent.

But residents of the area have circulated flyers saying, "We don't need to sacrifice home sites to commercial speculators in this county."

The 300 acres involved are now officially planned for residential development. Three separate applications have been filed by different developers seeking to change that designation to office or industrial.

Those proposals are generating protests from those who live in nearby single-family homes in the Reston and Vienna areas. Residents of 39 subdivisions representing more than 2,000 homes have formed the Hunter Mill Defense League to fight commercial development.

The proposed changes to the land plan were filed as part of this year's review of the county land-use plan.

Boston Properties has asked Fairfax to change its residential plan for 147 acres in the southeast corner of the interchange to commercial to allow for more than 2.25 million square feet of office space in 17 buildings. That plan also includes a small section of single-family homes.

Robert Thoburn, once an active Republican politician and former owner of a Christian school, and his son, John Thoburn, have asked for a change from residential to industrial on two large tracts totaling 111 acres. The Thoburn properties are on the north side of the interchange and on both sides of Hunter Mill Road.

W. Chin Lee has asked the county to approve changing an eight-acre site adjacent to one of the Thoburn parcels from residential to industrial. Approval of the Thoburn and Lee applications would produce at least another 2.25 million square feet of office space.

The Fairfax County Office of Comprehensive Planning has tossed in another 75 acres now planned and zoned residential, known as the McMann tract, that it says should remain residential.

The Thoburn and Boston Properties planners and designers teamed up and have proposed major traffic improvements for the interchange and other sections of Hunter Mill Road. A new loop road skirting the proposed commercial developments is planned. That loop would connect existing Sunrise Valley and Sunset Hills avenues via a new bridge over the Dulles road corridor. Developers said they plan to build two new access loops at a new interchange they plan to build connecting the loop road to the toll road. That would create a new toll booth between the Leesburg Pike and the existing Hunter Mill Road exits.

Developers also have proposed constructing a connector road between Hunter Mill Road and Route 7. That connector would come into Route 7 east of Baron Cameron Avenue, the main entrance road from Route 7 into Reston. According to Richard Keller of Keller Co., a Tysons Corner-based transportation consultant, developers have agreed to pay for all proposed road improvements.

If approved, the Boston Properties project alone would generate approximately $30 million for the Fairfax County tax base in the next 10 years, according to attorney Ed Prichard, who represents Boston Properties.

He said development at the existing planned residential zoning could produce a net loss of $3 million over the same period. Prichard was speaking to the Centreville Task Force, a group of citizens appointed by Centreville Supervisor Martha Pennino to study and make recommendations on numerous proposed land-use changes in the booming Centreville area.

Prichard said noise from the Dulles road makes the Boston Properties site "not usable for single-family" home construction because of setbacks required by the county to provide proper noise protection. Prichard said the Boston Properties plan would provide a "westward gateway for Reston," with the Center for Innovative Technology as a gateway on the east.

William J. Keefe, chief of the comprehensive plan branch of the county's Office of Comprehensive Planning, said his staff has considered the proposals for the interchange properties in four different areas -- transportation, land use, environment and economics.

"The proposals could work environmentally. The economic situation is at least a plus with $30 million added to the tax books. I can't imagine a Fortune 500 company that would turn it down," Keefe told the Centreville group.

However, the staff said the plan does not look on the land use and transportation aspects with favor. "The staff comes down hard on extending commercial to Difficult Run," Keefe said. Difficult Run is a major stream valley running through western Fairfax.

The proposals call for more than 4 million square feet of commercial space, which "equals one third of that planned in the 50/66 corridor" in Fairfax Center, Keefe said.

He said the county has been dedicated to "lines of demarcation where residential should end and commercial begin. Four million square feet is a hell of a lot of space."

Keefe said the proposed development would generate at least 8,000 peak hour car trips per day.

"Hunter Mill Road cannot handle it. What happens to Sunrise Valley and Sunset Hills?" Keefe said.

Planners representing both the Thoburns and Boston Properties spoke at the Centreville meeting. Task force Chairman John Thillmann, who is also a member of the county's planning commission, commended both groups. "You have done a marvelous job of putting it together. This is one of the most professional presentations I have seen in 15 years," of working for and with the county. Thillmann is a former county staff member.

But professionalism was not under study. Land use was, and the citizens group and Thillmann voted to recommend that the planning commission and the board of supervisors deny the proposals.

Grayson Hanes, an attorney representing the Thoburns, took their case Tuesday to the Dranesville Task Force, which is studying land use changes in that district. Part of the Thoburn land is in the Dranesville District.

"This area of the county has a long history which merits a land use change," Hanes said. Hanes is a member of the law firm of Hazel, Beckhorn and Hanes.