Supervisor Martha V. Pennino, a well-known Democrat who is seeking her sixth term on the Fairfax County board, and Linda Douglas, an up-and-coming Republican and a community activist, are giving voters one of the most colorful matchups in this fall's election.

Neither comes from a political family; Pennino is the daughter of an illegal Bulgarian immigrant and a summer camp director, and Douglas, who was born in Hawaii, is the daughter of an enlisted man in the Navy and a registered nurse. Each, however, is highly valued by her party in the battle to represent the Centreville District on the County Board of Supervisors.

Centreville encompasses a large chunk of western Fairfax, including Reston, the Town of Vienna and the fast-developing Rte. 28 corridor near Dulles International Airport.

Because there are so many newcomers, many of whom are expected to vote Republican, in the 110,000-resident Centreville area, the GOP believes it has a better chance than ever to capture a seat that has long seemed undisturbedly Democratic.

"A lot of people just want to see a change," said Douglas, 42, a former congressional aide who was vice chairman of the Fairfax County Republican Committee. "I'm offering them one."

But Pennino, 69, a Democrat so popular in 1984 that many urged her to run for Congress against Rep. Frank R. Wolf (R-Va.), does not believe it's time for the GOP.

"This candidate has no record of accomplishment," Pennino said of her Republican challenger. "When I first ran {for the board in 1968}, I had been elected three times to the Vienna Town Council. Frankly, I think {Douglas} has been in the board room twice and stayed about 20 minutes."

Douglas counters with a long list of activities that begins with her membership on the county Human Rights Commission and the Reston Community Association. She was a key figure in the ouster last year of county Republican Party Chairman Benton K. Partin, who was viewed as ultraconservative, and the election of former county sheriff James D. Swinson. She also worked for Wolf as his Centreville organizer in 1984 and 1986.

Douglas' ties to the Republican Party have helped her campaign bank account. As of Aug. 15, she had almost matched Pennino in fund raising with $30,900, of which $10,500 came from the county party, according to Douglas' campaign manager, Starr Brooke. Pennino had raised $32,400, most of which came from small donations.

Healthy finances, Douglas' political organizing experience and her aggressive campaigning -- since March, Douglas has been shaking hands at bus stops, shopping malls and front doors -- have raised her name recognition.

Still, Pennino didn't win the recognition as Washingtonian of the Year in 1986 by The Washingtonian magazine or the nickname of "Mother Fairfax" by slouching.

Pennino won the praise of many residents in December when she supported a measure that would have restricted the amount of office construction permitted in land zoned for industrial uses. That measure, which business leaders fought long and hard, was defeated on a 5-to-4 vote by the county board.

Douglas said she would not have supported it. "It was done too hurriedly and it didn't address our transportation problems," she said.

Though she says Pennino has brought too much subsidized housing to Reston, Douglas said the county needs more affordable housing for teachers and young families.

Traffic, however, is clearly the number one issue.

For years, Pennino, a member of the Northern Virginia Transportation Commission, has advocated road and rail improvements, particularly along the Dulles Access Road corridor. Douglas, a member of the Reston Transportation Committee, advocates increased bus service to heavily traveled centers, staggered work hours and reversible road lanes that would change with the commuter traffic.

Apart from transportation, several Republicans say there is another major issue, one they have dubbed the "energy issue" -- Pennino's age and stamina. The Democrat would be 73 years old at the end of the next term.

"I don't think age is the issue," Douglas said. "It's a matter of energy, time and commitment. Centreville needs a lot of attention and, frankly, she hasn't been providing it."

Chuck Weir, Republican Party chairman in the 10th Congressional District, said Pennino "does not seem well." Many others noted that her voice often cracks, making her seem ill. Weir said, "The biggest problem she has is getting around the district. She can't sustain a vigorous campaign."

Fairfax Democratic Chairman Harris Miller said that is not true. "Martha still gets around. She goes wherever there are three people gathered."

Pennino points out that President Reagan is 76 years old. And her voice cracks, she explained, "when I go through periods of stress and strain" because of a bout with polio when she was 9 years old.

The polio temporarily paralyzed her left arm and right leg and affected her throat, but the only lasting effect, she said, is her "weak throat."

"I question whether {Douglas} has more stamina," Pennino said. "I would match her energy any time. I play tennis. I ski. I ice skate. I bowl. I swim."

Pennino says the question the voters will have to ask Nov. 3 is: " 'Who can do the most for us?' I've got the connections. I've got the clout . . . . What has my opponent got besides being very pretty? This is not a beauty contest."

Miller assessed the race this way: "My sense is Linda Douglas is working for the future . . . . Martha will have to retire sometime." But now, he said, "she has broad and deep support."

But Republicans say they believe Douglas has an excellent chance of upsetting Pennino.

Between May and October, 6,000 new voters registered in Centreville. "We always used to lose in Reston, but since 1984 it's gone Republican," Weir said.