Bob Burnett, who sells automatic garage door openers, and Arthur Dykes, a certified public accountant, turned their car slowly onto Valleycrest Boulevard in Annandale the other night and surveyed the scene. Some residents in the middle class enclave known as Broyhill Crest had outdoor lights shining brightly, and occasional flickers of television sets could be seen through living room windows.

But outside all was quiet and not a person was in sight, just the way crime watchers Burnett and Dykes liked it.

Crime has not disappeared in Broyhill Crest. But it has diminished to such an extent that there usually is no sign of trouble when Burnett and Dykes or one of the 50 other teams of their Fairfax County neighbors take turns on night patrol looking for someone breaking into a home or for a teen-ager vandalizing one of their cars.

Burnett, Dykes and several thousand other Washington-area residents, the region's police chiefs among them, are convinced that the army of citizens participating in such Neighborhood Watch programs played a major role in reducing crime in every jurisdiction here last year. Of the larger jurisdictions, the overall drop in crime ranged from 3.3 percent in the District to 17 percent in Arlington, while the number of burglaries decreased even more substantially.

No one knows exactly how many people are participating in the programs, but aparently there are more than 2,000 Neighborhood Watches in the region, some of them covering only a city block, others more than 1,000 homes in suburban subdivisions. Police say almost all the groups have sprung up in the last four years and their number is steadily increasing.

Police chiefs here say these newly formed legions are recreating chapters from a bygone era, when neighbors knew their neighbors, seemed to care about their comings and goings and called the police when they spotted a problem.

They are not armed vigilantes and only rarely have they personally apprehended suspects and held them for police. What they have done, besides posting the ubiquitous signs announcing the presence of the Neighborhood Watchers, is create a psychological deterrent to crime in many neighborhoods, police say.

Police have coached them to be nosy in a productive way, to make a conscious effort to look out for the suspicious vehicle casing the neighborhood, the passer-by who seems up to no good, or just about anything else that's out of the ordinary.

As a result, residents often call with concerns about allegedly suspicious individuals, or perhaps a front door left open, that prove to be unfounded. But police say they are not upset by the time invested in pursuing those reports because they believe information gained from the ones that do check out more than offsets the inconvenience of investigating the others.

The Neighborhood Watch program was instituted nationwide in 1972 by the National Sheriffs' Association. In the Washington area, the most elaborate program seems to be in Fairfax County, where police Chief Carroll D. Buracker says that on any given day about 1,000 people are driving through their neighborhoods on the lookout for crime.

Most street corners in those neighborhoods have blue-and-white Neighborhood Watch signs with large, skeptical-looking eyes painted on them as a warning to would-be criminals that someone may be watching. If the Fairfax patrollers spot something amiss, they call in a report on their CB radios to a base station operator who in turn alerts police.

In Broyhill Crest, Marion (Red) White, a retired Army colonel, supervises 113 residents who either drive through the 954-home neighborhood once a month or sit by a base station radio to collect the reports filed by the patrollers.

He said that with the advent of the community's Neighborhood Watch, the number of burglaries, larcenies, vandalism incidents and auto tamperings has dropped from 63 in 1981 to 34 last year. His patrollers are credited with the recovery of a stolen D.C. car parked in the neighborhood and once spotted a fire just outside some Fairfax school offices.

"We're not going to prevent everything," he said. "But we have made a distinct contribution for our neighborhood. The criminal element knows we're out there. We're just augmenting the police coverage, not replacing it."

"The time commitment two hours a month is so minor compared to the benefit," said Dykes.

Residents in other jurisdictions occasionally drive through their communities looking for crime as well, but mostly they've signed on as watchers from their homes, pledging to keep their eyes and ears open for a thief, a vandal, a mugger.

Despite the acclaim for the Neighborhood Watch programs, police acknowledge that the citizen efforts in one community often only serve to shove the crime to another, unpatrolled neighborhood. Says Arlington police Chief William K. Stover: "It's fair to say you do displace some crime. But you do that with other programs as well."

Fairfax's Buracker said he worries that as crime drops, watch groups will lose interest, as has happened in some communities such as Bowie, where police say a driving patrol ended when a particular run of crimes subsided. "Keeping the momentum is a real challenge," Buracker said. Toward that end, Fairfax now has an annual recognition dinner to honor its citizen patrollers.

"I can't say enough good things about it," Stover says. "There's no question about the effectiveness. It's helped us immensely." Arlington burglaries dropped by 33 percent last year.

In Montgomery County, Sgt. Howard Miller of the crime prevention unit said that some information provided through a Neighborhood Watch helped lead to the arrest of Timothy J. Buzbee, who is accused of several rapes in the Aspen Hill area.

"For years police went along with the idea that crime is our problem," Miller said. "Now we're saying that crime is a police and community problem."

Prince George's Police Chief John E. McHale describes Neighborhood Watch as "a great program." He noted that four years ago one Seat Pleasant community, plagued by a rash of burglaries, started a Neighborhood Watch program and has not had a break-in for the last three years.

In Fairfax County, where there are 328 patrols, there were fewer burglaries last year than 10 years ago, even though the population increased by 128,000 during that period, Buracker said.

"Undoubtedly, the Neighborhood Watch is the single reason for the drop in crimes against property," Buracker said. "If I had to replace those citizens with officers, it would cost $30 million. Obviously we wouldn't do that. But to get the same kind of results we'd have to."

In neighborhood after neighborhood throughout the Washington area, police and their part-time assistants cite firm statistics, or sometimes just their instincts, to account for the drop in crime after a Neighborhood Watch was started.

In McLean, an extensive study by five residents showed that crime dropped substantially more in areas covered by Neighborhood Watch programs than in those with no patrols. Using 1980 and 1981 crime statistics, the study examined communities with 6,724 homes covered by Neighborhood Watches and communities with 33,020 homes that did not have the citizen patrols.

The difference was striking: Burglaries dropped 18 percent in non-watch areas, 42 percent in those with patrols; vandalism remained the same in non-watch neighborhoods and was cut by 23 percent in Neighborhood Watch areas; auto thefts were cut by 25 percent in patrolled areas and remained the same elsewhere.

In Alexandria's Warwick Village community, where a Neighborhood Watch program was started in 1979, the number of burglaries dropped from 47 that year to eight in 1981, the last year for which statistics are available.

Along either side of upper Georgia Avenue NW in the District's 4th police precinct, officers Herbert Smith and Eartha Hicks of the community services unit said crime has dropped in some blocks as residents have initiated Neighborhood Watch lookouts.

"Neighbors are nosy," Smith said. "We're trying to make that nosy person proud of it, to put that nosiness to use."

They have done just that in the 500 and 600 blocks of Quintana Place NW, where $65,000 duplexes line the street. Two years ago, residents noticed some drug selling on the street corners, substantial truancy, an occasional break-in and sporadic vandalism.

"I decided we'd lick the problem," said Mary Sanford, a 40-year-old nurse at the National Institutes of Health. The answer was a Neighborhood Watch--no car patrols, just visual vigilance, an occasional call for police help and bright orange-and-black street signs warning, "This neighborhood reports all suspicious activity to the Metropolitan Police."

The result, she said, is that "we haven't had anything but flowers stolen in the last year."