Installation delays have put Northern Virginia's 911 emergency telephone system on hold once again, as the area nears completion of a 10-year effort to start the special service.

The emergency dialing system, which had been set to start Sept. 1, will be delayed at least a month until early October, according to Thomas Brannan, spokesman for the Northern Virginia Planning District Commission, which has helped organize the service. Brannan warned that it could take an additional two months to train operators and put the complex system in working order, pushing the opening to early December.

"We're refraining from setting another completion date," said Brannan. "We'll believe it when we see it. We're not going to be raising people's expectations again for nothing."

The new system will allow residents to dial just three numbers -- 911 -- to report fire, police or medical emergencies. Northern Virginia jurisdictions participating in the system will be Arlington, Alexandria, Fairfax and Loudoun counties, Fairfax City, Falls Church, Leesburg, Middleburg, Vienna and Herndon. The District of Columbia and some Maryland counties have had 911 service for almost a decade.

In Northern Virginia -- as in many areas -- jurisdictional rivalries, bureaucratic hassles and technical problems have stymied attempts to open the 911 lines. One of the most difficult technical -- and political -- hurdles was devising a system that would divert emergency calls to the correct jurisdiction. Since areas served by the C&P Telephone Co., whose lines will be used for the system, overlap political boundaries, cooperative contracts between all Northern Virginia jurisdications and the phone company were required before actual work to implement 911 began.

The final holdout, Alexandria, decided to join the program last November, paving the way for contract negotiations with the telephone company.

However, once the political headaches were cured, local officials discovered they needed a custom-made switching system to handle the large number of separate fire and police departments serving the area.

Although officials had predicted last spring the system would open July 1, it was delayed until Sept. 1 to allow time to receive the new switching system. Assembly of that equipment by a California manufacturer is running slightly behind schedule, creating the latest delay in beginning the service, Brannan said.

Loudoun County, however, actually began 911 service July 15 because it didn't require the complex call-transfer equipment needed by the larger counties.

Proponents of the emergency number claim it is a quick and convenient way for residents to get emergency help from fire and police departments. However, opponents in some areas contended the time required to switch 911 callers to the proper fire and police jurisdictions would take longer than dailing directly on a conventional line.

The 911 system will cost the Northern Virginia governments a total of $150,000 for installation and operating costs the first year, and $143,600 annually for the next three years, according to Brannan.

Costs for individual counties in the first year break down to Fairfax, $53,500; Arlington, $44,500; Alexandria, $29,400; and Loudoun, $22,500. Incorporated towns will pay a percentage of the bill charged the county surrounding them. For example, Fairfax City will pay a portion of the Fairfax County costs, Brannan said.