From left, John Guevara, John L. Litzenberger Jr. and Brian Schoeneman. (John Guevara; John L. Litzenberger Jr.; Brian Schoeneman for supervisor)

Twenty-four years have passed since Republican Michael R. Frey became supervisor of the newly created Sully District in western Fairfax County. Now, Frey is retiring, and the once-rural area, which has become a hub for businesses and immigration, must launch a new political era.

The first step comes Saturday at Westfield High School in Chantilly. Three Republican candidates will compete for the nomination in a firehouse canvass that is expected to draw about 2,000 voters from a population of 130,000 residents.

The candidates — John Guevara, John L. Litzenberger Jr. and Brian Schoeneman — are all more conservative than Frey, who has not endorsed anyone. Whoever wins will face Democratic nominee Kathy Smith — a longtime School Board member who has pushed for more schools funding — in November’s general election.

Although Sully has known only a Republican supervisor, it leans Democratic in state and national races, backing President Obama in both his White House bids and Sen. Mark Warner (D-Va.) last year.

But the supervisor’s race has focused mostly on local issues that resonate through much of Fairfax: clogged roads, crowded schools and cultural rifts triggered by the steady arrival of Asian and Latin American immigrants in historically white neighborhoods.

“We are in the city now,” said Denise Benedict, 52, as she stood on her porch in Chantilly one recent day. She complained about cars speeding through quiet streets, and a nearby drug problem that recently led to a heroin ring bust.

Frey’s successor will be one of at least two new members on a county Board of Supervisors where Democrats hold a 7-3 majority; the other open seat is in the heavily Democratic Mount Vernon District, where supervisor Gerald W. Hyland is retiring.

In Sully, the Republican hopefuls have campaigned by scouring lists of consistent Republican voters who they believe are most likely to participate in the canvass, which runs from 10 a.m. to 4 p.m.

Each candidate enters the election with some advantages.

Guevara, a Mexican American, received a letter of support from the state Republican Party chairman, John Whitbeck, who says he wants more diversity in the party. Schoeneman, a former electoral board secretary, has raised the most money — $21,700 since January. And Litzenberger, a member of the county Planning Commission, has been a fixture in Sully politics nearly as long as Frey.

The candidates praise Frey, who remains popular, even as they argue that he and the rest of the board allowed property taxes to get too high and roads to become too congested.

They also break with Frey on dealing with residents’ concerns related to new immigrants — such as the mostly Guatemalan day laborers who crowd in front of the Centreville public library in search of work. While Frey — who helped establish a nonprofit labor center for the workers — asserts that the men have a right to stand on the corner, the three candidates all say they’d explore ways to clear them out.

“If it came to me to make it illegal to stand in front of the library, I would support that 100 percent,” Guevara, 41, said to applause at a recent candidate’s forum.

The most pressing issue for Sully voters is traffic.

When Schoeneman met Patricia Crowley, 80, she complained about years of unfulfilled promises to fix the often clogged intersection of Routes 28 and 50 in Herndon. “I don’t think they ought to say they’ll spend the money if they don’t mean it,” said Crowley, as Schoeneman nodded in agreement.

Litzenberger said that as a planning commissioner, he knows how to pressure developers into helping to pay for road improvements. “Not one penny in taxes is used in those proffers,” he said.

Schoeneman said that he would push for more projects to relieve congestion. Guevara faulted the planning commission for past failure, a viewpoint Litzenberger called naive in a region that is still growing.

On county taxes, all three advocate freezing tax rates or rolling them back.

Guevara, an IT manager at the AT&T Consulting Services company, wants to eliminate a business, professional, occupational license tax in the county — known as the BPOL tax — that generates about $150 million per year for Fairfax.

He says he would boost the tax base by luring more large employers into the area, which that is primed to benefit from development plans near Dulles International Airport.

Schoeneman called eliminating the tax impractical without finding a way to replace lost revenue.

He, in turn, has been criticized by the other candidates because he has lived in the Sully District only since January. Guevara also has criticized Schoeneman, 37, for having ties to organized labor — he is legislative director of the International Seafarers Union, and some workers have contributed to his campaign.

“How often do you see Republicans working for unions?” said Guevara, 41. “There’s a big difference here, in whether the party goes moderate, to the left or remains conservative.”

Litzenberger, who at age 64 is a generation older than his opponents, calls them both inexperienced. “In eight years, they would be where I was in 1983,” he said.

On a recent day, Guevara knocked on the door of the Chantilly home of Christina Dingman, a sixth-grade teacher. Although she is a reliable Republican voter, she gave him an earful about nearly flat teacher salaries in the county — a result of the still-anemic local economy and a concern more typical among Democrats.

“I’ve gotten less than $5,000 in raises over the past seven years,” Dingman said. “There are young teachers out here who can’t make it.”

Guevara, caught slightly off guard, talked about the need for growing the county’s economic base. Then he moved on to the next voter.