Fairfax Democratic supervisor candidate Catherine M. Hudgins spent many hours at community meetings and homeowners associations in Reston and Vienna, patiently explaining her two campaign themes to voters in a quiet, non-confrontational way.

She told voters in the Hunter Mill District that they should be angry about gridlock caused by four years of office and town house construction. And--without mentioning her opponent by name--she said they might want a supervisor who was a bit less adversarial.

Then, a week ago, she pounced on the Republican incumbent, Robert B. Dix Jr.

In a mailing to voters, she likened Dix's behavior to that of a screaming toddler. It featured a picture of a crying child with the phrase "Bad Behavior" on the cover. Inside were the words "Even Worse Behavior," with newspaper headlines including "Angry Dix Blasts Supervisors and Media" and "The Wrath of Supervisor Dix."

Yesterday, members of both parties credited that sharp-tongued attack for helping Hudgins, a first-time candidate for office, beat Dix soundly in a surprise victory. Along with her message about growth and traffic, which resonated with voters, the late focus on Dix's reputation for abrasiveness pushed her to victory, they said.

"Cathy discovered everywhere she went that people were unhappy with Bob Dix," said Hudgins press adviser Janice Spector, a longtime Democratic strategist. "Dix could be volatile at times. He was not cooperative at times. He made himself vulnerable by the way he conducted himself in public."

Dix did not return telephone calls yesterday.

Republican Rep. Thomas M. Davis III, a longtime friend of Dix's, attributed Hudgins's win to an energetic campaign. He said Hudgins tapped successfully into an anti-growth sentiment, and he said Dix made the mistake of resting on his laurels.

"She ran a good campaign," Davis said. "She hustled. Bob tried to just be the incumbent." Another Dix adviser said he felt Dix's supporters, including many in and around Vienna, stayed home Election Day because they didn't think Hudgins had a chance of beating him.

Dix's ouster was part of a widespread victory for Democrats in Fairfax County on Tuesday. Voters said goodbye to the county's Republican sheriff and to an incumbent Republican state senator, and several Democratic legislative candidates were successful.

And Democrats increased their majority on the Board of Supervisors--from six to seven--as a result of Hudgins's win. Democrats now hold every countywide office except clerk of the Circuit Court.

"They had a bad night in Fairfax County," Democratic Supervisor Gerald E. Connolly (Providence) said of the GOP. "The Democrats outsmarted them and out-organized them. The Republican Party is split with factions and division that has crippled their ability to put a unified message before voters."

Democratic Board of Supervisors Chairman Katherine K. Hanley said she would use her new 7-3 majority to build on achievements made in the past five years.

"We will continue to make sound fiscal decisions," she said. "We will continue to make education a top priority. We are going to continue reorganization and streamlining of government. We are going to continue in the direction that we were going."

Hudgins, a former Hanley chief of staff and a longtime Reston activist, pledged yesterday to open a dialogue with residents and business officials in the Hunter Mill District.

"People have to feel that their input is valued," said Hudgins, 55, who is married and has two grown sons. "To be an effective leader, you must know how to incorporate diverse views. I think the community measured me against the current supervisor."

In the Reston area--particularly near the Dulles Toll Road, where dozens of new office buildings have gone up in the past four years--voters gave Hudgins the overwhelming nod. In some precincts in those areas, she won by more than 2 to 1 over Dix.

Hudgins said people are tired of traffic on Wiehle Avenue, Reston Parkway and Sunset Hills Road. She said Dix did little to address the issue of synchronizing traffic signals on those roads and other transportation-related problems.

"People are very, very concerned about what will happen in the future with growth and development, how it's going to affect their quality of life," she said.

During the campaign, Dix responded that he'd worked hard to improve traffic flow in the area and to press the state for road improvements.

Business leaders, some of whom backed Dix with more than $200,000, said yesterday they were stunned by his loss.

Mark Looney, a spokesman for the Fairfax County Chamber of Commerce, said the growth of the high-tech community in that area--including new buildings for Oracle, BDM, Andersen Consulting, Nextel and other firms--prompted the backlash among Reston residents.

"You had a lot of things that were planned actually coming to fruition in the last four years," Looney said. "It tested the patience of those who live [in] and have to navigate that area daily."

Members of both parties said the Hudgins victory shows what can happen when a challenger combines the right message with the right amount of door-to-door-style campaigning.

"Cathy did exactly what she had to do to win," Hanley said. "She went out and knocked on doors. She went into the community. She went to meetings and talked to voters. When all is said and done, that's what campaigning is all about."

CAPTION: Newcomer to elective office Catherine M. Hudgins (D), right, gets a victory hug from Emilie F. Miller, chairman of the Fairfax County Democratic Committee, after Hudgins's upset victory over two-term Supervisor Robert B. Dix Jr.

CAPTION: Democratic board Chairman Katherine K. Hanley, who was reelected to her position, lays out her goals at her office. "We will continue to make sound fiscal decisions," she said. "We will continue to make education a top priority."