Fairfax County Supervisor Audrey Moore, the most vocal proponent of public disclosure laws on the county board, said yesterday she probably violated the law by voting for a rezoning application without reporting that her son worked for the developer's transportation consultant.

The consulting firm, Planning Research Corp. (PRC), was listed on an application filed with the county last year by the Centennial Development Corp., which was seeking approval for a mixed-use commercial and residential complex near Fair Oaks Mall. Moore's 25-year-old son Douglas is a janitor at PRC.

The county public disclosure law requires supervisors, before participating in a land use case, to reveal whether they or members of their families have a business or financial relationship with the applicant in the case. They also must reveal whether such a relationship exists with any person or firm performing consulting work for the applicant or otherwise benefiting from the application.

Although two supervisors, including one of Moore's chief adversaries on the board, said she did not violate the law, Moore said it was her responsibility to disclose.

"Whether the law required it or not, I should have disclosed," said Moore, an Annandale District Democrat. "I didn't realize that PRC was involved. All I can say is that I'm sorry and that I'm embarrassed."

Board Vice Chairman Martha V. Pennino (D-Centreville) said she believes such a disclosure was unnecessary and added that Moore's critics were trying to make the public disclosure law appear frivolous by charging violations where none exist.

"Her son working as a janitor had no financial interest in that project," Pennino said. "The purpose of the disclosure law is to ascertain who has a financial or business interest with an applicant or consultant or who stands to gain from a particular project."

Supervisor Nancy K. Falck (R-Dranesville), who has clashed repeatedly with Moore on numerous countywide issues, defended Moore yesterday. "I can't see that that's a conflict at all," Falck said when asked about the PRC case.

Moore said that PRC was not Centennial's transportation consultant when the rezoning case first came before the board two years ago and that she did not realize the firm eventually was retained by Centennial.

She said, however, that she was making no excuses. Moore disclosed her son's relationship with PRC when the firm sought the board's approval for a county contract in an unrelated case. She also abstained from voting on that request.

Despite her personal dilemma, Moore said her support for the disclosure laws remain unchanged.

"This hasn't changed my point of view," she said. "These are good laws and I'm going to argue for them as hard as ever. I'm just embarrassed that I didn't disclose in this case. I was wrong."

Until yesterday, Moore had remained unscathed from the month-long ethics controversy that has touched every county supervisor except the newest board member, Katherine K. Hanley (D-Providence), who was elected this month.

The most serious case involves Republican Board Chairman John F. Herrity, who is scheduled to stand trial Aug. 21 on a charge filed by the county prosecutor. Herrity was charged with violating the state public disclosure law last winter for his role in the county's review of a major rezoning case involving a developer who was Herrity's real estate partner.

Six other supervisors became embroiled in the controversy when the Fairfax Journal reported that they had voted on rezoning cases without revealing that they had received 1983 campaign contributions from applicants or their consultants. Earlier, The Washington Post reported that Herrity had participated in five development cases without disclosing that the applicants or their consultants had contributed to his 1983 campaign.

Fairfax Commonwealth's Attorney Robert F. Horan Jr., a Democrat, said last week that he would not prosecute Herrity or the other supervisors for failing to disclose the campaign donations, saying he had found no evidence that their actions were intentional.

As the public furor over the alleged violations intensified, Herrity derisively referred to Moore as "St. Audrey" because she was singled out in news reports and editorials as the lone supervisor with no apparent violations.

Herrity did not return a phone call placed to his office yesterday.

Moore's son's job with PRC was revealed by an Annandale resident, Dr. Louis Blazy, who said Moore was using the issue for political purposes. He said he is considering challenging her in the 1987 election.

Horan could not be reached for comment yesterday on the PRC case. The maximum penalty for violation of the county law is a six-month jail term and a $500 fine.

Pennino, although contending that Moore's alleged lapse in the Centennial case was not a violation, said it showed that "all of us here on the county board are human."