A Virginia judge has promised to dismiss an assault charge against Loudoun County Sheriff Donald L. Lacy in one year provided the controversial sheriff avoids trouble in the meantime.

The ruling in effect puts Lacy on probation for one year without convicting him. As a result, the sheriff will have no criminal record because of the case, according to his attorney.

The decision handed down Friday by Rappahannock County Circuit Court Judge Rayner Snead came after Lacy, who was appealing a lower court conviction on the same charge, entered a plea of no contest.

"If he behaves himself, that's it," said Richmond Commonwealth's Attorney Aubrey Davis, a special prosecutor assigned last year to investigate the sheriff. Lacy's attorney, Louis Koutoulakos of Arlington, agreed. "I don't know of anything else" facing him, Koutoulakos said.

The 35-year-old Lacy, who was attending a state sheriff's convention in Virginia Beach yesterday, was restrained but pleased. "I'm happy with it," he said. " . . . But what happens in my personal life is really my own business."

The misdemeanor charge stemmed from a New Year's Eve incident in a motel lounge near Dulles International Airport. Two young women claimed Lacy verbally abused them after they took his photograph at a dance there. Later, they claimed, he took one of them by the arm and led her to the hotel lobby where he attempted to have her arrested by two sheriff's deputies.

Lacy was subsequently convicted on the charge in Fauquier County General District Court and fined $100. That conviction was automatically voided when Lacy appealed to the higher court.

Lacy, whose term expires next year, is currently facing a petition drive, the goal of which is to force his removal from office. Earlier this year, a special grand jury issued a report recommending that Lacy, the first Republican elected sheriff in Loudoun, resign because of his private conduct and personal abuses of power.

The special grand jury, however, was not empowered to indict him. For his part, Lacy charged that its report was part of a smear campaign against him.