A Prince William County Circuit Court judge yesterday placed Bull Run Water Works, a privately owned water system that has been criticized for frequent disruptions of service, under the trusteeship of county authorities.

After county and state officials testified about recent troubles with the water system, which serves about 300 homes on Bull Run Mountain in the northwestern part of Prince William, Judge H. Selwyn Smith ruled that the waterworks' assets and daily operations should fall under the control of the Board of County Supervisors for an unspecified period.

The corporation's president, Paul Baugher, and other stockholders will retain ownership of the waterworks.

"I'm thrilled," said Mary Jane Zimmerman, one of about 10 Bull Run Mountain residents who attended yesterday's half-hour hearing at the courthouse in Manassas. "The last time the water was out I had a 9-day-old baby. It was very difficult for us."

Virginia officials filed suit last month, asking that Bull Run Water Works be ordered to comply with state regulations or that a trustee be named. The state acted a few days after customers of the waterworks had their water flow cut off or reduced for three days. The county later joined in the lawsuit.

Under yesterday's order, which went into effect immediately, local officials will contract with the Prince William County Service Authority to operate the water system; the court is to review the status of the waterworks every three months.

The lawsuit alleged that the waterworks was financially troubled and frequently inoperable.

Baugher, who did not attend yesterday's hearing and could not be reached for comment, has said previously that under normal conditions the system works properly but that residents, particularly those with swimming pools or lawn-sprinkling systems, contribute to its problems. Also, he has said that the county is attempting to buy the company for less than he believes it is worth.

County officials say no decision has been made to purchase the system, although they are studying such an action. In addition, the county has filed a suit claiming that the waterworks owes about $60,000 in back taxes. Baugher has disputed the amount of taxes owed.

Ryland Bailey, a senior engineer with the State Corporation Commission, which oversees privately owned water systems, said yesterday that Bull Run Water Works has received an estimated $112,000 in fees annually.