Members of the Prince William Board of County Supervisors upbraided the county administration yesterday because they were not promptly notified that the 911 emergency system broke down for 45 minutes last week, leaving callers with a busy signal.

A severed cable in the 911 system and the subsequent failure of a backup line left calls for police, fire and emergency medical service unanswered in Prince William and the cities of Manassas and Manassas Park beginning at 2 p.m. on Feb. 8.

However, county supervisors were not notified until more than a week later, in a written memorandum that some supervisors said yesterday they had not received.

No efforts were made to publicize the breakdown until Wednesday, when officials in charge of the 911 system were queried by The Washington Post, which learned of the failure through an anonymous tip.

"The board members should have been notified when {the breakdown} occurred," said Supervisor John D. Jenkins (D-Neabsco), adding that he intends to address what he sees as foot-dragging with County Executive Robert S. Noe Jr.

Noe was out of town yesterday and could not be reached for comment.

Larry Hughes, a deputy county executive, said that prompt notification of the elected officials "usually would be done. It should have been done." One reason it wasn't, he said, was that an unrelated power outage struck the county government center the day after the 911 failure, preoccupying officials there.

Hughes and other county officials have blamed the breakdown on Contel of Virginia Inc. They said Contel had falsely assured them that the recently improved system was "redundant," so that even if one line was severed -- as it was when an electrician at Potomac Mills mall accidentally sliced the cable -- the emergency calls would travel to dispatchers over another line.

Katherine M. Lueckert, director of Prince William's Office of Telecommunications, said she has not heard of any deaths or serious incidents during the 911 failure, and believes that none occurred. She said the county had planned to release details of the incident to the media next week after Noe had written a letter to the president of Contel complaining of the breakdown.

Hughes said that Contel has told the county that both the primary and backup features of the 911 system are now working, and that Contel has promised to conduct tests of the backup system.

Lueckert said Prince William and the two cities hope to acquire the ability to conduct regular tests themselves to ensure that the 911 system is in order.

Five members of Prince William's seven-member board said yesterday that they wished that the county administration had notified them immediately of the 911 breakdown, rather than relaying the news in a memorandum. Board Chairman Kathleen K. Seefeldt (D-Occoquan), saying she was not yet fully informed, said the 911 failure "certainly has to be looked into," but declined further comment. Terrence Spellane (I-Coles) could not be reached.

Two supervisors, Democrats Hilda Barg (Woodbridge) and Edwin C. King (Dumfries), said they had heard nothing of the 911 failure until contacted by a reporter.

"It seems to me that we should have been notified within an hour or so" of the failure, King said.

Staff writer Pierre Thomas contributed to this report.