The first thing they tell you is that they are not vigilantes.

"All we armed with are flashlights and pencils," says Bill Bowen, prime organizer of the Villamay subdivision security patrol. "Our job is to observe and report, observe and report. The police do the rest."

Villamay is a handsome, upper middle class neighborhood about two miles south of Alexandria off the George Washington Parkway. Many of the attractiev brick homes sit on sprawling, terraced lawns that give panaromic scenes of the Potomac River and the city's monuments.

Nightly, from just before dark to upspecified morning hours, two civilian patrol cars weave around the well-tended neighborhood, about a mile square, looking for anything that appears suspicious.

"Watchdog One calling Rover Two, come in, please," squawks the CB radio in one of the patrol cars, this particular one a sleek brown Jaguar. Rover Two, who was a Navy captain Thursday night, checks in with Watchdog One to report that everything is all right. Two Watchdogs are assigned to CB base stations each night to receive the rovers' calls and keep records of suspicious activities noted by the rovers.

The Villamay Security Patrol was started three years ago by the Villamay Community Association to counteract a rash of silver burglaries in Villamay and surrounding neighborhoods.

"We still have burglaries; in late 1975 and early '76 they were even a little heavier. Some of these crooks are professionals. They can listen in on our radio conversations," Bowen said. "But we feel patrolling is helping to deter Villamay crime in general."

The Fairfax County Board of Supervisors endorsed the idea of citizens' patrols earlier this week after being told by the county police department that such groups help reduced vandalism and burglaries of homes.

Nearly 130 residents, out of about 280 households in Villamay, are volunteer patrollers who rotate canvasing the neighborhood about once every two months. The community assocation invested about $500 in two CB radio sets for the patrolling chore, but many residents also have bought their own sets. Thirty Villamay residents, many of them also patrollers, take turns operating the CB base station three nights a row about every six weeks.

Fairfax police records show that since the security patrol began, burglaries have increased in the geographical whose greater half if the Villamay subdivision. The records show three were 24 burglaries during 1976, compared with the 14 burglaries in 1973.

"Bu there's no telling if the increase is happening with Villamay or in other neighborhoods within this area," said a police spokesman.

On the other hand incidents of vandalism and larceny, which would include crimes like stealing bicycles or plants from a front porch, have decreased in the same area since the security patrol started. There were 34 larcenies in 1973, compared to 22 incidents in 1976, and there were 27 incidents of vandalism reported in 1973, compared to 23 reported in 1976.

"Still, there's no telling what burglaries and other crimes we might have had without the patrol," Bowen said.

Officer Art Mabry of the Groveton police district in Fairfax County agrees with Bowen: "I think the patrol has discouraged crime, especially teenage crime. In Fairfax, at least, most of your break-ins are by teen-agers who live in the same general area. They used to just keep an eye out for the blue and gray of the Fairfax police. With the patrol going on, they don't know who to look out for, and that has seemed to lessen the problem."

Mabry admitted that police were concerned at first that the patrol would turn out to be a vigilante operation.

"We don't want any vigilante groups," he said. "But I think this patrolling system is a good idea when it works cooperatively with the police."

He said the police also were afraid they would be called in "for every little thing," but that the patrollers have turned out to be "sensibly discrimanating."

Capt. Bill Arnold, who spent a couple of hours Thursday night driving his Jaguar at about five miles an hour to inspect winding streets and cul-de-sacs, says he enjoys patrolling "once in a while."

"It's almost relaxing, actually," he said. "You're advised not to confront anybody even if you do see something, so it's not dangerous. And its the kind of thing that makes you feel like you're doing something good without being a do-gooder.

Many of the patrollers are military men like Arnold, or retired military. Bowen says their backgrounds make them "perfect for patrolling. They're dependable, and a lot of them have backgrounds in radio. A retired Air Force colonel, George Carey, operated the tiny CB base station.

Bowen says no patroller has sighted a break-in occuring, but that patrollers have alerted police to strange cars and people in their neighborhood.

Groveton district police say similiar neighborhood patrols are operating in the Belle Haven and Pinewood subdivisions. Villamay patrol organizers say they were first, but police say the Belle Haven ad Villamay patrols "were born about the same time."

Patrolling has brought some side benefits to Villamay. Bowen said, Sharing patrol duteis has brought neighbors close together, he said. Kids playing all over the neighborhood recognize the patrollers by the CB antennas and tease or chase after them.

"People who never knew each otehr before talk to each other now," Bowen said.

"It's made the whole neighborhod more security conscious," he added. "Before, people were looking around, but they didn't know if they were looking at something suspicious or not. Now they're paying attention to what's going on.

"We want people to know we're here, we think our presence helps discourage crime," Bowen continued. "The patrols used to have rubberized signs to put on their cars, but they were stolen about two months ago. We have to get some others and watch them more carefully this time."