John F. Herrity, the outspoken Republican Fairfax County board chairman, has agreed to debate Audrey Moore, the equally outspoken Democratic county supervisor who has been daring Herrity to do so for six months.

However, the two durable Northern Virginia politicians, who disagree on a host of issues relating to development and growth, also disagree on what they will debate on Friday.

"They're both being pretty bullheaded about what they're going to talk about," acknowledged Tim Sayles, managing editor of The Springfield Independent and Burke Herald, who is arranging the debate for the Northern Virginia Press Club. "They're not going to listen to me anyway."

Moore, who opposes rapid growth in Fairfax County and believes that county policies unfairly favor developers, said the debate will be on the merits of growth. She said that Herrity, whom she first challenged to debate in early June, will be a formidable opponent.

"Obviously, I don't think he's got the right of the issue, but he's very good," Moore said. "From my point of view, he's been pulling the wool over people's eyes for ten years."

Herrity said the debate will concern the Springfield Bypass, a proposed 35-mile highway that would curve through the outer reaches of the county, and possibly the county's fiscal picture. He said that there is no point in discussing growth, especially during a recession.

"Talking about growth is like talking about the weather," Herrity said. "It's out there, and what can you do about it?"

The Republican board chairman said he was more interested in debating someone from the Greater Washington Research Center, which issued a report two weeks ago predicting budget deficits in Fairfax. Herrity called the report "dishonest and wrong."

But Philip M. Dearborn, the author of the study, said that he will be in New York on Friday, when the press club will meet at the Springfield Hilton.

Robert S. McNamara, former secretary of Defense and World Bank president, headed the task force that issued the report. "He's not going to be available either, I'm sure," Dearborn said.

"If those people don't have enough guts to come in and defend their study," Herrity said, "their credibility is going to be hanging out there."

Dearborn said that he plans to send a written response to Fairfax County's complaints about his study.