Arlington police officers have a new companion when they cruise the streets on the lookout for crime. Perched by their right elbow is a $5,000 minicomputer terminal which puts information from national and state crime teletypes at their fingertips.

Except for their occasional maddening beeps, the computer terminals have won converts in officers like Janet Scaman, who, at the push of a button, now can get names, addresses and other information flashed onto the computer's TV-like screen. "You don't have to worry about driving and writing at the same time," said Scaman.

The computers save time and, according to Police Chief William K. Stover, they can also save lives. In a matter of minutes, an officer can check whether a car is stolen or has been involved in a crime. "I like my officers to know who they're stopping," said Stover. "That's our first concern -- officer safety."

The computers also make it easier for police to act on their hunches, to run checks on suspicious vehicles without tying up the police radio channels and the dispatcher back at headquarters. According to Capt. John Bassett, commander of the emergency communications center, three stolen vehicles were identified by the computer in its first week of operation.

And, said Stover, a motorist stopped by police will no longer have to wait 10 to 15 minutes for an officer to complete a routine license check which in precomputer days would be relayed over the busy police radio, passed by the dispatcher to the teletype operator and radioed back to the officer.

Finally, the transmission of messages and information via computer can bypass people -- including criminals -- who listen to police radio scanners. Officers can send messages back and forth without worrying about being overheard.

The computer terminals, with keyboards and screens, have been operating in 15 Arlington police cars for more than two weeks. They're the first of their kind in the Washington metropolitan area and the latest technological weapon in the county's computerized game plan.

The patrol car terminals, manufactured by Motorola, are one aspect of a computerized dispatch operation installed last April in a carpeted, noise-proof room at police headquarters as part of a $1.8 million project designed to coordinate, simplify and speed up the county's emergency operations. Of that sum, $700,000 was spent on computers.

Arlington's first goal, now accomplished, was to get police and fire dispatchers working together in the same room so they can share information and coordinate their efforts.

But the bigger test will come Dec. 15 when the county and most of Northern Virginia go to a regional "911" telephone system that will allow residents of several jurisdictions to dial one easily memorized three-digit number and get a response from local police, fire or emergency rescue teams.

Craig Allen, a former dispatcher who has become the police department's in-house computer expert, said the new computers should be a major factor in avoiding an overload for call-takers and dispatchers when 911 goes into effect. Arlington is now braced for at least a 25 percent increase in calls as citizens take advantage of the simple emergency number.

With their computers, Arlington's police and fire dispatchers can get an instant report on the status and location of their vehicles. For the 15 police cars equipped with computer terminals, for example, status is reported by simply pushing a button to indicate "en route," "at the scene" or other positions.

Then, given a street address for a reported incident, the computer can determine available units, although, according to Allen, the final decision will always remain with the dispatcher -- the "human factor," as he calls it.

If there are two locations with the same address -- there's a 5501 S. Columbia, for example, in Fairfax and in Arlington -- the computer can come back with a quick query, allowing police to check back with the caller.

For dispatchers and officers, the computers took some getting used to. "People were really scared at first," said Allen. "There was so much to know. But now they're getting really good. They can show me some tricks and shortcuts they've figured out themselves."

According to Stover, early reports show that computerized dispatching has cut one or two minutes off the average time it takes an Arlington police unit to respond to a call, now down to less than five minutes. That may change with the rush of calls on 911, but at least "we're ready," said Allen.