Fairfax County's new 911 emergency communications system does not work adequately, officials said yesterday. Despite the problems, they said, all emergency calls are being answered swiftly, on average in 1.1 seconds.

"We're having trouble with telecommunications," said Lt. Col. Michael W. Young of the Fairfax County Police Department, which operates the communications center. "This is not the way we intend to run the center. We do not find the present system acceptable."

The extent of the problems, or who is to blame for them, was not precisely defined yesterday. Richard A. King, deputy county exec- utive for public safety, said the "automatic call director" had been malfunctioning and causing the new system to go down periodically.

Last Friday, Young said, the primary telephone system broke down and a backup system was used for about half an hour, he said. He said there were no delays in emergency response.

A spokesman for American Telephone & Telegraph Co., one of the contractors for the project, said the company is "now working with the county on isolating problems as they occur. When these problems are identified as being AT&T, and not someone else, we are doing our best to resolve them as quickly as possible."

The new system, which is housed in the police department's Pine Ridge facility, is supposed to provide call-takers with a visual display of the phone number and the address and automatically verify information, assign a priority to the call and relay the information to the appropriate dispatcher.

A police source said yesterday that the public is getting through, but that call-takers are having to rely heavily on the manual backup system, which was used at the old Emergency Operations Center in the Massey Building in Fairfax City. He said staff members at the new emergency operations center were literally "making it work."

During the transition to the new system, residents said they were having trouble getting through. A Herndon resident said she dialed 911 but "no one answered the phone." Another resident said that he tried to report a stolen car and that the line went dead after ringing several times.