The campaign to unseat Fairfax County Supervisor Robert B. Dix Jr. by a former aide to the county's top Democrat already has generated sparks.

This week, it got even hotter with the entry of a third candidate.

John Thoburn, a conservative Republican who owns a string of religious schools in Fairfax and Loudoun counties and has battled Dix (R-Hunter Mill) for years over the right to develop Thoburn family land near Reston, formally entered the race as an independent on Tuesday.

Vowing to oust his nemesis from the office he has held for almost eight years, Thoburn said yesterday, "It's time to term-limit Dix."

County Democrats hailed Thoburn's decision to run as a boost to their party's candidate, Cathy Hudgins -- A former aide to county board Chairman Katherine K. Hanley (D) -- saying Thoburn's conservatism will siphon support from Dix.

Thoburn's decision to run continues a family legacy in local politics. He, his father, and his brothers have all run for various offices, and the elder John Thoburn served one term in the Virginia House of Delegates.

For more than a decade, the Thoburns have waged planning and zoning battles with Fairfax officials about the locations of their schools. More recently, John Thoburn has attempted to develop family-owned property in the fast-developing Dulles corridor into a miniature golf course.

Thoburn has argued to no avail that the location of the property next to a major interchange is perfect for more intense development.

Dix and Thoburn often have clashed at public meetings, sometimes getting into heated arguments about land rights. Thoburn blames the supervisor for thwarting his efforts to develop his property.

"It's a dramatic example of how a supervisor can let their own personal biases get in the way," he said. "I think voters are going to see Bob Dix has it backwards. He's trying to slow down recreation growth while he speeds up commercial development."

Yesterday, Thoburn also attempted to focus on broader issues, saying that he opposes the use of taxpayer money to spur growth, and promising to invest more heavily in road improvements in the Hunter Mill District if he is elected.

Dix played down the importance of Thoburn's announcement, saying that he has enough bipartisan support to fend off a challenge from another conservative.

And he said he believes in a mix of development, pointing to the combination of homes and offices in Reston. "I believe that we have provided the example of managed growth and smart growth," Dix said.

Dix also criticized Thoburn's nearly decade-long efforts to develop his property in the face of community opposition. He said Thoburn has been treated fairly by the county and refuses to accept defeat gracefully.

"His style is one that is very aggressive," Dix said. "He attempts to get his own way through threats and intimidation. That does not work with me. I'm not afraid of him."

Hudgins declined to comment on Thoburn's candidacy. Her campaign has attacked Dix for allowing growth to run rampant, pointing to the many office buildings being constructed along the Dulles Toll Road in Reston.

Republicans, meanwhile, expressed confidence that Dix will weather the challenges from both the left and the right.

Joseph Underwood, the GOP chairman in Fairfax, said that Thoburn's focus on developing his own land will help crystallize Dix's support for slower growth when he thinks it makes sense.

"You've now got a rampant pro-growther in the race, and its not Bob Dix," he said. "It's John Thoburn."