Fairfax County School Board member Kate Hanley announced yesterday that she will seek a seat on the Fairfax County Board of Supervisors in a special election July 15.

Hanley, a Democrat, joins Republican Del. Stephen E. Gordy in the race to fill the Providence District seat that Democrat James M. Scott is vacating June 3.

Scott, who has represented the district since 1972, said last week he was resigning from the nine-member board to become director of community relations for the Fairfax Hospital Association.

Robert Beers, an aide to Supervisor Thomas M. Davis III (R-Mason), also is seeking the Republican nomination, although he has not yet formally announced his candidacy.

In an interview, Hanley, 43, said she would bring "the perspective of an experienced citizen" to the board.

Appointed by Scott to the School Board in 1984, she has been active in a range of civic associations and school groups, and was a vocal advocate for higher teacher salaries during this year's school budget deliberations. She is considered an easy favorite for the Democratic nomination.

County Planning Commission member Rosemarie Annunziata, another Democrat who had been considering a race, said yesterday she had decided not to run. Hanley said Annunziata, a lawyer, would serve as her campaign treasurer.

Hanley said she hoped to raise $20,000 to $25,000 in her campaign for the supervisor post, which pays $21,589 a year.

In the 1983 general election, more than 14,000 people voted in the Providence District race for supervisor, out of 38,488 registered. Although there are now 44,540 registered voters in the district, analysts are predicting that the short campaign and mid-summer polling date will result in a turnout of fewer than 10,000 voters in the special election.