Virginia's two leading candidates for governor campaigned in Fairfax County yesterday and said they plan to devote more resources and time to capturing the state's largest bloc of voters.

Democrat Timothy M. Kaine rallied a crowd of more than 200 students at George Mason University, while Republican Jerry W. Kilgore stood beside business leaders in Tysons Corner to highlight his endorsement last week by the political arm of the Fairfax County Chamber of Commerce.

"We've long said we wanted to see the day when Northern Virginia was a battleground," Kilgore said at the chamber, calling his recognition as the race's "pro-business candidate" a sign of his appeal to centrist voters in Fairfax. "Well, it's turning out to be a battleground."

Kaine, the lieutenant governor, credited supporters in the county of 1.1 million people with helping narrow his opponent's lead in the polls in recent weeks.

"This part of the state is so important to us," Kaine said to his Northern Virginia supporters at the start of a day-long swing that included stops in Newport News and Lynchburg. "It is so important. The work that you have done here. . . . You have given us the momentum to succeed. We have caught this race up from a big gap. We have the steering wheel in our hands, and we are not letting go of it. We are in control of this race now."

The candidates set up strong field operations in Fairfax months ago. Kilgore has two offices in Fairfax City and a dozen staffers, and Kaine has one in McLean.

The challenge in the race's final stretch before the Nov. 8 vote will be to appeal to an electorate that swings left and right, depending on the office and the issue, a big political middle ground between more liberal inner suburbs and more conservative outer ones.

Democrats dominate local offices in Fairfax; the congressional delegation is split; and, last year, John F. Kerry became the first Democratic presidential candidate to carry the county in 40 years.

Mark R. Warner (D) won Fairfax in the 2001 gubernatorial campaign, and so did his predecessor, Republican James S. Gilmore III. The county's delegation to the General Assembly in Richmond splits about evenly, with Democrats representing districts inside the Capital Beltway and Republicans outside it.

The county added 25,000 jobs last year but has trouble finding places to put new homes for those workers. A growing immigrant community struggles to afford rising housing prices.

Kilgore's chamber endorsement drew responses from across the political spectrum.

Four former chairmen of the chamber wrote a letter to its executives protesting the endorsement, saying that Kilgore opposed two of the business group's top priorities: tax reform in 2004 and the transportation tax referendum in 2002.

The anti-tax Virginia Club for Growth also protested the endorsement in a statement that said Kilgore bowed to pressure from the chamber not to oppose efforts to raise regional taxes.

One political certainty has existed for the past century: The winning candidate for governor has carried Fairfax.

Kilgore, the former attorney general, said yesterday that he "will be spending a lot of time in Fairfax" in the next month, focusing on several issues his strategists believe will resonate with county voters. They include his pledges to widen Interstate 66 inside the Beltway and allow local governments to raise their own taxes for rail and road projects, his attention as attorney general to fighting gangs and his stand against illegal immigration.

"I think I'm being underestimated in Fairfax County, and that's just fine with me," Kilgore said.

Kaine said he plans to spend about 35 percent of his time between now and Election Day campaigning in Fairfax and the rest of Northern Virginia.

His strategists see Kerry's nearly 35,000-vote margin in the county as a sign that the increasingly urban county is drifting Democratic. Yesterday, the candidate offered a transportation plan with likely appeal to Fairfax voters, pledging to give local governments the power to reject rezoning proposals if they determine that nearby roads could not handle traffic from the new development.

Kaine said the county's importance was brought home to him the moment he entered the George Mason student center yesterday morning with his son, Nat, a high school sophomore, and was greeted by Board of Supervisors Chairman Gerald E. Connolly (D).

Connolly asked Nat, "What do you have to remember about this race?" Kaine recalled. "Nat repeated the line that Gerry has drilled into his head: 'It's all about Fairfax. It's all about Fairfax.' "

Larry J. Sabato, director of the University of Virginia Center for Politics, said it is inevitable that the Fairfax streak in statewide races will come to an end some Election Day. "All it is going to take," he said, is a "close election won by a Republican in which Fairfax County voted for the Democrat."

Speaking before a crowd at George Mason University, Democrat Timothy M. Kaine said Northern Virginia has "given us the momentum to succeed."Republican Jerry W. Kilgore, shown here on Saturday at Virginia Tech, touted his Fairfax Chamber of Commerce endorsement yesterday in Tysons.