Fairfax County supervisors, among Northern Virginia's most ardent supporters of a sales tax increase to finance new roads and public transit, spent last week trying to decipher the tea leaves left by voters.

Fairfax defeated the tax referendum by a sound 54.5 percent to 45.5 percent, a margin larger than that in Arlington or Alexandria (both 51 percent to 49 percent) and smaller than those in Prince William (59.5 to 40.5) and Loudoun County (64 to 36). In two Fairfax magisterial districts, Braddock and Dranesville, the measure went down in every precinct. It fared best in Reston and Tysons Corner, areas that stand to benefit directly from a proposed rail line to Dulles International Airport.

Back in May, the seven Democrats and three Republicans elected to run Washington's largest suburb were the first local leaders to endorse the half-cent sales tax increase. Only Michael R. Frey of Sully, a Republican who represents Fairfax's conservative western flank, withheld his support. Along with Gov. Mark R. Warner (D) and local business leaders, the board, led by Chairman Katherine K. Hanley (D), vouched to civic groups and parents that raising taxes was the best hope to uncork the county's traffic congestion.

"I'm still in a grieving stage," said Supervisor Sharon S. Bulova (D-Braddock), who pushed the tax measure in newsletters to constituents. "We need to regroup. . . . I'm concerned about the failure of the referendum from the point of view of understanding why people voted no."

Many Northern Virginia voters indicated a disdain for higher taxes and suburban sprawl that they feared new roads could create.

The county is largely built out, meaning that only small pockets of land remain for development. Yet Fairfax voters seemed as concerned about sprawl as did their neighbors to the more rural west. And a revolt against zooming property tax assessments showed its strength last week, suggesting tough decisions ahead for a county government with a reputation for generous spending.

"I'm tired of paying taxes," Margaret Downing, 66, a retiree from Springfield, said on Election Day. "As soon as you build a new road, it's no longer efficient. I'm sure something needs to be done, but not on my nickel."

Supervisors' immediate problem will be finding money for road improvements while funding $1.7 billion for school construction over the next decade.

"We're using most of our [borrowing] capacity right now for schools, and that will be the first priority," Hanley said.

But supervisors are likely to face problems when they run for reelection next year: equal-opportunity retribution against Democrats and Republicans from the anti-tax Republicans who emerged victorious last week.

"Sure, for trying to do a good job, we'll be targeted," said Elaine N. McConnell (R-Springfield). She proposed the sales tax increase almost three years ago. She laughs off the solutions offered by her fellow Republicans that involve finding more state road-building money: "Whatever extra we get, it won't even do a third of an intersection in my district."

Most leaders in the anti-tax fight hail from Fairfax, including two newly elected state senators from Centreville and Clifton. They are promising to make Fairfax politics very interesting next year.

"You'll see Republicans rising up to run on an anti-tax-and-spend theme," said Sen. Ken Cuccinelli, elected to represent the 37th District.

Not so fast, say some of the board's Democrats. Remember County Board Chairman Thomas M. Davis III? When the Republican took office in 1992, he quickly got behind a campaign to raise the local meals tax. The proposal went down, 55 percent to 45 percent.

Two years later, Davis was elected to Congress.