Fairfax County Board Chairman John F. Herrity will make a bit of political history today when major Washington television stations start running his commercial, the first-ever over-the-air noncable television advertisement in a local Northern Virginia political race.

The 30-second spot, previewed yesterday for reporters, will run for two to three weeks during prime viewing hours on all four major Washington area stations: WRC (Channel 4), WTTG (Channel 5), WJLA (Channel 7) and WUSA (Channel 9). The total cost of the spots, which will run periodically during the morning, afternoon and evening, will be $40,000 to $50,000, according to Herrity campaign officials.

Herrity, a Republican, has been chairman of the County Board of Supervisors since 1976. He is being challenged by Supervisor Audrey Moore (D-Annandale). The election is Nov. 3.

In the ad, a fast-paced series of snapshots race across the screen as a voice-over touches on Fairfax County's job growth and "bright economic future" before focusing on road projects Herrity has supported. The ad lists I-66 and the Dulles Toll Road as well as a number of transportation projects still largely on the drawing board, such as the Springfield bypass, the outer beltway, commuter rail lines and a mass transit link to Dulles International Airport.

"That's why Herrity," the announcer says. "The good work he's done is all around us."

Two radio spots ran for Herrity in June. He is expected to have at least one or two more television ads before Election Day.

Moore, whose campaign has raised significantly less than Herrity's, has not yet decided to buy air time for advertisements. A Moore spokesman said yesterday that the campaign is "in the process of pricing radio, television and print ads."

Moore campaign officials have said they will produce a television ad if they can afford to air it.

The ad reflects Herrity's strategy of making transportation the primary issue in the campaign. He has consistently steered clear of the development issue, where Moore's longstanding efforts to slow the pace of growth may give her the upper hand with voters tired of the stream of new office buildings and shopping malls.

"Jack knows that Audrey can't win on transportation, and he knows that he can't win on development. So he wants the ball in the transportation court," said one county Republican who asked that he not be identified.

Herrity's advisers are eager to draw attention to Moore's record of having opposed several major transportation initiatives.

"I don't think Audrey could put a commercial like this on today because she hasn't shown any leadership on transportation," said Tom Herrity, the candidate's campaign manager and son. "The contrast is fairly evident."

Moore spokesman Janice Spector replied: "Mrs. Moore could produce a very fine documentation . . . that shows that Fairfax County has been grossly mismanaged in terms of the development and transportation issue. The reason we are in bumper-to-bumper traffic today is because of the lack of leadership by Chairman Herrity."