Patty Struck, a 911 emergency phone operator for Fairfax County, remembers the man whispering into the telephone that there was an armed robbery in progress. She remembers asking him where, and having him reply, "The Exxon gas station on Backlick Road."

"I said, 'Where on Backlick Road?' and he just repeated, 'The Exxon station on Backlick Road! Hurry!' " Struck said, shaking her head. "There must be eight Exxon stations on Backlick Road."

Struck finally got a more specific location from the man, but not before the loss of precious moments in which a police officer could have been on the way.

The incident is a classic example of the most agonizing and frustrating aspect of being the person who answers 911.

With all of the police and rescue power of the county poised to render assistance, nothing can be done for someone who cannot tell an operator where to send help. Soon, however, technology will overcome the mental paralysis that often accompanies a critical emergency.

Fairfax County, as well as all other area jurisdictions, is in the process of acquiring a new, more sophisticated system called Enhanced 911 that will give 911 operators the address and number of the phone from which an emergency call is made. The information will appear on a computer console in front of the operator as soon as the 911 line is answered. The push of a button will send that information to a dispatcher for transmission to an officer or a fire rescue unit.

Enhanced 911 means that almost as soon as a legitimate emergency call is taken, police or rescue units can be on the way. Fairfax County's system will even recommend the nearest available units to a dispatcher.

With this technology, even those unable to talk -- heart attack victims, those being robbed and who do not want the robber to know police are being summoned -- need only dial 911 and leave the phone off the hook long enough to be answered in order to bring aid.

The new technology, partially in place in Prince George's County, is expected to be in operation by January 1986 in Fairfax, by fall 1986 in Arlington and Alexandria and perhaps as early as July 1985 in Montgomery County. Enhanced 911 is the system D.C. Mayor Marion Barry last month proposed that the city acquire as soon as possible.

"We're excited," said Fairfax County's deputy police chief, Col. Alan Barbee. " . . . This will certainly eliminate some of the problems we have now."

The department has not always been so forthright about the system's shortcomings or sanguine about their solution. In 1981, an internal police study was sharply critical of management of the facility.

The department refused to make the report public, and after a supervisor said he gave it to a Washington Post reporter, angry police officials demoted the man. The county went all the way to the 4th U.S. Circuit Court of Appeals to defend its disciplinary action and refusal to make the report public.

Fairfax County's present Emergency Operations Center (the combined 911 switchboard and police and fire dispatching center) is a windowless, low-light chamber 10 feet underground in the basement of the Massey Building, the county headquarters.

Operators sit in front of consoles with buttons for 300 phone lines, including 47 incoming 911 lines, as well as direct lines to area police and fire departments and hospitals, to Washington Gas Light Co., Vepco, the jails, even the CIA.

In 1983, the 78 operators, who are paid between $14,700 and $23,800 a year, took 243,438 emergency calls.

They fielded 692,411 nonemergency calls, requests for weather information, for directions, for information about shelters for the homeless, about what to do about errant beavers and raccoons, about how to find out if there is a warrant for your arrest, about how to cook a baked potato in a microwave oven.

On a recent night shift, there were eight operators for police and fire and five dispatchers.

A young boy's voice comes over the 911 line.

"I've got someone checking," the boy says.

"Checking what?" says the operator. "What is your emergency?"

"No. Checking! Checking! Someone checking!" And again the operator asks what the emergency is.

"Checking, you know, like, can't breath, something stuck in the throat. Checking!"

"Choking!" says the operator. "Hold on for fire rescue."

The call is transferred with the press of two buttons to the county fire rescue dispatcher, a process many emergency callers find unnerving.

"Yeah, the reaction is, 'My house is burning down and they are putting me on hold!' ," said Debra Godwin, one of two assistant supervisors for the emergency center's night shift.

But they are not. As it stands, those actually taking 911 calls are on the police side of the 911 operation, and if the emergency is a fire or a request for rescue, the call is transferred instantly to a fire operator.

With the new system in place, all 911 operators will take all types of calls and route them by computer to the appropriate dispatcher.

The system will be able to provide histories of the addresses at which a problem is reported, so officers or firefighters on the scene will know if there is, for example, previous domestic violence at that address or toxic chemicals in the basement.

And it will instantly provide case numbers and enter the call in the department computers, processes now done by hand many hours after an incident occurs.

"The point is not to replace human judgment," said Barbee, "but to provide technology where it is appropriate, to provide more information more quickly . . . .

"This will still require judgment, good judgment on the part of the people, and they will still be working in a stressful environment," he said. "We just hope these changes will make it less stressful."