After months of searching, Fairfax County Democrats have found a candidate willing to run against County Board Chairman John F. Herrity, a Republican, in the fall elections.

Vivian Watts, a former president of the county's League of Women Voters, announced she will seek the Democratic nomination at the party's May 29 nominating convection.

"I have tried to resist, but a number of people have encouraged me to run." Watts, 39, said yesterday. She is the only person to seek the nomination to run against Herrity, 47, who has served on the board since 1972.

Emilie Miller, head of the county's Democratic Commitee, said she had encouraged Watts, an Annandale resident, to seek the office. "We wanted someone ereditable and Vivian is. She can beat Jack [Herrity]," Miller said.

Miller said she called "a lot of people" the past few months seeking a Democrat to oppose Herrity, one of the county's best-known politicians.

Miller said yesterday she does not expect any candidate as strong as Watts to seek the nomination. She said Anthony T. Lane, vice chairman of the Fairfax school board, considered running for the board chairman's seat but withdrew in favor of Watts.

If anyone else signs up, Miller said, "I'm going to ask where were they when we were looking for candidates."

Watts, who is married and has two children, worked previously as director or research and legislative activities for the county's Chamber of Commerce.