The executive director of the Virginia-based Airlie Foundation yesterday accused federal prosecutors of harassing the organization and its employes to satisfy a "personal vendetta" as they press a federal investigation that follows the conviction of the organization's founder.

In a letter to U.S. Attorney W. Williams, Airlie's Frank J. Kavanaugh charged that "unnecessary abuse" by agents of the Department of Justice, the FBI and the Internal Revenue Service had contributed to family problems, divorce and premature death among approximately a dozen persons associated with the Warrenton foundation.

"Agents of the federal government under your direct supervision have continued to pursue a largely fabricated case through an unconscionable assault on innocent associates of mine and the Airlie staff," said Kavanaugh in the letter, which he released to the press yesterday.

Williams yesterday characterized Kavanaugh's charges as "ludicrous" and "totally unfounded," but declined to discuss them further. "I am not in the position to comment on whether an investigation is or is not going on at this time," he said.

The founder and former executive director of the 20-year-old Airlie Foundation, Dr. Murdock Head, was convicted last year on charges of engaging in a criminal conspiracy. Head, 56, is free on a $5,000 personal recognizance bond while he appeals his conviction and three-year prison sentence. Head has since said that the IRS has begun an investigation into alleged civil tax fraud that could jeopardize the foundation's tax-exempt status.

The Warrenton-based foundation, located on 1,700 acres of farmland in the Blue Ridge Mountains, conducts conferences for federal and private organizations. During its lifetime, it has received more than $15 million in government contracts and grants.

Kavanaugh said yesterday that federal agents had repeatedly misrepresented key aspects of the case to his staff members, and threatened them with indictment if they did not cooperate. He said similar tactics by government agents had contributed to the premature deaths of Edwin Bain, who had been counsel for the foundation, and John Slater, a Florida man who had been a financial supporter of the foundation.

"There seems to be continuing vendetta to find some crime or crimes that can additionally be fitted to Murdock Head and the foundation," Kavanaugh said. "They're just out to try and do to him civilly what they were unable to do criminally."