Democratic Supervisor Audrey Moore yesterday began a $120,000 television advertising blitz in her race against Fairfax County Board Chairman John F. Herrity. The hardest-hitting of her five commercials criticizes Herrity for supporting a "reckless development policy" that amounts to "dropping the entire city of Newark right on top of our neighborhoods."

In that ad, as a photograph of Newark office buildings drops with a resounding thud on a map of Fairfax, a voice says: "Thanks for nothing, Jack."

Moore's 30-second ads will run 100 to 120 times on the major networks, during such popular shows as "60 Minutes" and "Wheel of Fortune." They also will run frequently during evening newscasts.

The biggest surprise in the ads is that they attack Herrity, a Republican seeking his fourth term. Last week, Moore said her commercials would be "positive," "factual" and "on the issues."

Tom Herrity, who is running his father's campaign, said Moore's ads were far from positive and "typical of the doubletalk and hypocrisy we have seen from Audrey Moore during the campaign."

Michael J. Ellis, a communications specialist who produced Moore's commercials, said they were not negative, but rather "comparison ads" in which Moore and Herrity are prominently featured.

He differentiated them from Herrity's commercials, which Ellis said were "straight attack ads." Those commercials, which ran earlier this month, used a large photo of Moore on the screen next to the words "No, No, No." Then, a voice said the Democrat had voted against every major transportation improvement, including I-66 and the Dulles Toll Road. Herrity's name was mentioned in those ads for only a moment and only in small print at the bottom of the screen.

That "no, no, no ad," as it was called, was credited with cutting into the substantial lead Moore held in early polls. Before it was broadcast, Moore was leading by 14 points among likely voters; afterward, she was ahead by 7 points.

Tom Herrity noted that when his father's ad attacking Moore's road record was released, a spokeswoman for Moore said the negativism was a "sign of a campaign in trouble."

Herrity has been off television for a few days, apparently saving for a last-minute spree and deciding which ad to run in the final days before Election Day, Nov. 3.

Tom Herrity would not comment on how much money his father's last broadcast blitz will cost or what it will say. He did say it will begin early this week.

Moore's early broadcast advertising was confined to radio and until recently, it was unclear whether she would be able to afford any television time. She said, however, that by "saving her pennies" and holding off until the final week before the election, she could afford the costly ads.

Ellis said the "Thanks for nothing, Jack" ad is a "raw" comparison of the amount of traffic and people that have come to Fairfax under Herrity's progrowth policies.

Herrity was elected to the Board of Supervisors in 1971 and elected chairman in 1975.

Since 1970, county figures show that office space has increased fivefold to 41 million square feet, and the number of housing units has doubled to 260,000. In addition, Fairfax's population has grown by 200,000 since 1970; it is now more than 710,000.

According to the latest census figures, Newark has 314,000 residents.

Moore's four other ads show:

Former Virginia governor Charles S. Robb in his McLean back yard saying, "You don't have to agree with Audrey Moore on every issue regarding Fairfax County to admire her courage and her tenacity."

A photo of Herrity beside a traffic jam with a voice blaming him for "supporting every major high-density development project in Fairfax County."

Citizens vouching for Moore's honesty and saying that she would improve the county's quality of life.

A shrinking picture of Herrity and a enlarging photo of Moore as a voice says Moore is the only candidate who fought to balance development and the county road system.