Two incumbents on the Prince William Board of County Supervisors staved off fierce intraparty challenges in primary voting yesterday, winning the right to defend their seats in the Nov. 3 general election.

In the Dumfries District, where two of Prince William's best-known Democrats squared off in a bitter contest, incumbent Edwin C. King beat Floyd C. Bagley, chairman of the county Democratic Party and a former member of the Virginia House of Delegates, 56 percent to 44 percent. King will face independent Norma Pandazides, a federal worker, in the general election.

In the Gainesville District, incumbent G. Anthony Guiffre, a Republican seeking a second four-year term, edged civic activist Helen E. (Betty) Duley 40 percent to 37 percent. IBM engineer John W. Dempewolf Jr. received 23 percent.

Guiffre will face Manassas real estate agent Robert L. Cole in November. Cole defeated Claude J. (Brad) Bradshaw 54 percent to 46 percent in the Democratic primary yesterday.

The Dumfries and Gainesville races were the most visible in a busy primary season in Prince William, where 13 candidates were running in six contests in four of the county's seven magisterial districts.

In the Brentsville District, two party veterans beat lesser-known challengers in a bid to succeed Democrat Joseph D. Reading, who is retiring after two terms.

In the Democratic race, Manassas lawyer Norborne P. Beville Jr. defeated supermarket clerk Richard W. Mechalske 58 to 42 percent. On the Republican side, retired businessman William J. Becker trounced Carroll A. Weimer Jr., a Manassas lawyer, 63 percent to 37 percent.

In eastern Prince William's Woodbridge District, businesswoman Hilda M. Barg overwhelmed Lucian L. Johnston 76 percent to 24 percent in a Democratic primary contest that drew little countywide attention. Barg will face Republican Ella Shannon, a member of the county Planning Commission, and independent Edward Rodriguez in November.

Last night's results climaxed a primary season in Prince William that at times assumed a circus atmosphere, with the four magisterial districts serving as so many rings in which an apparently record number of candidates, including some of the county's most colorful politicians, performed.

Predictably, common campaign themes were transportation and development, with resentment against what many citizens consider rampant growth running higher than it has in years, according to local political observers.

The King-Bagley race in Dumfries attracted the most attention, pitting two former Democratic allies against each other in a highly personal and sometimes bitter contest.

"I think it was a matter of two well-known politicians locking horns . . . and I may have worked harder," King said last night. "Now I just hope I can win his supporters in the general election."

During the campaign, Bagley, a 65-year-old lawyer, claimed King was inaccessible to his constituents and had been acquiescent in approving undesirable developments.

King, 58, said that both charges were ludicrous and that he was running on his record, which includes a stint as county board chairman last year. On development, King said he has a talent for hard-nosed negotiations with developers, insisting that they make concessions, such as building roads and other public facilities, before their projects are approved.

Dumfries is one of Prince William's most diverse districts, including established communities along Rte. 1 such as Triangle and Dumfries, home of many blue-collar and lower-income families, along with newer, affluent areas such as the large Montclair subdivision.

Across the county, in Prince William's rural western end near Bull Run Mountain, the Gainesville District incumbent, Guiffre, 44, faced a stiff challenge from the 52-year-old Duley and Dempewolf, 41, who lost to Guiffre in the GOP primary four years ago.

The two challengers accused Guiffre of being remote from his constituents and not forceful enough in representing the district's interests on the board. Candidates in both parties criticized the incumbent for allegedly ignoring residents in the Loch Lomond community near Manassas whose homes were flooded during heavy rains last summer.

Despite the criticism, Guiffre retained a core of support, most of it near his Catharpin home in the district's northern end, and was the front-runner going into the primary, according to many observers.

Like King, Guiffre now needs to mend fences with his opponent's supporters in time for the general election.

"Dempewolf's and Duley's supporters are conservatives, and I'll ask them to come over and support me," said Guiffre, who claims that his record also qualifies him as a fiscal conservative.

In the Democratic race, Cole, 46, anchored his hopes in the district's suburban southern end near Manassas; Bradshaw, a 52-year-old slow-growth advocate who lives near the Manassas National Battlefield Park, is a veteran of many development battles.

Cole's victory surprised many Prince William political analysts, who predicted that Bradshaw's network of rural civic activists would carry the day. Cole's strength around Manassas foreshadows a close race against Guiffre in the fall; like Bradshaw, the incumbent's greatest support lies in Gainesville's rural parts.

In Brentsville, the other Prince William district that retains large rural sections, both primaries pitted well-known candidates with strong backing from party regulars against new faces who were counting on grass-roots support.

In the Democratic race, Beville, a 46-year-old former county party chairman and two-time unsuccessful candidate for the Virginia House of Delegates, won the endorsement of retiring Supervisor Joseph D. Reading, the current county board chairman.

Reading made no secret of his contempt for Mechalske, 35, who waged a vigorous door-to-door campaign and whose greatest area of strength was thought to be Brentsville's primarily blue-collar areas near Manassas.

Beville said last night that the support of Reading and other established party figures was crucial to his victory.

On the GOP side, Becker, 67, also an unsuccessful candidate for the House of Delegates, was better known among party activists, although Weimer canvassed the district door-to-door. At 31, Weimer, a Manassas lawyer and former police officer, is the youngest candidate in Prince William this year.

In Woodbridge -- Prince William's most densely populated district, in the county's far eastern end -- Barg and Johnston waged a campaign that drew little attention elsewhere.

Barg, 53, had greater support among party regulars; Johnston cut a reputation as a gadfly who seemed to enjoy tweaking the noses of the incumbent supervisors, according to political observers.