At 9:30 p.m., the stillness of a summer night in Chevy Chase Village is shattered by the siren of a home secuirty alarm. A village patrolman is there a minute later, wading through bushes in search of a prowler.

The "victim" is a frail elderly woman whose home was once burglarized and who now sets off an alarm each time she imagines a break-in. On this night, she says, someone has stolen her her purse.

Officer Mark Woods knowingly winks at a bystander and waits for the woman to turn her back before picking up a bag lying on a nearby chair. "Oh there it is . . . I knew she wouldn't have taken it," she says. Apparently relaxed again, the woman thanks him graciously and says goodnight, and Woods returns to his rounds.

Although the situation is unusual, the quick response and the sensitivity shown by Woods are two major reasons why the 2,104 residents of Chevy Chase Village choose to pay over $215,000 a year for their own six-member police force, even though they receive full and -- by all accounts -- competent protection from Montgomery County.

Chevy Chase Village, an area north of Chevy Chase Circle that's home to some of the area's most affluent residents, is one of several dozen jurisdictions in the Washington area that have chosen to retain their own police forces despite the availability of better equipped and more sophisticated county police. In an era of centralized government, the existence of these small departments provides local residents with a sense of accountability and a small town accessibility often lacking in large suburban forces.

"What we've seen in this coutnry is the deterioration of the neighborhood police concept," said Chief Roy Burke, who also acts as the department spokesman and the city manager for Chevy Chase Village. "We provide personal services and have greater contact with our citizens. The neighborhood police concept is the way all departments should operate."

A running debate in law enforcementhad focused on the argument that citizens would be better served with the elimination or consolidation of such small police departments. A report by the National Advisory Commission on Criminal Justice Standards and Goals concluded in 1973 that "consolidation can frequently upgrade police service and lower cost.

"Because it is larger" the report continued, "the consolidated agency ususally has superior resources. Because it eliminates much duplication, it is usually less expensive -- citizens get more for their money."

But talk of disbanding their police departments piques most municipal oficials and citizens, who argue that nothing can compare to the security and rapport developed between officers and small communities. According to Robert Angrisoni, spokesman for the International Association of Chiefs of Police: "You get the most ferocious fight against consolidation from the town officials and citizens themselves. They may close down their schools before they close their police department.

"Small police agencies have a tremendous value. They are totally representative of the communities they serve. An officer that knows every back alley in his beat and the community he serves is very effective in crime prevention."

In the words of an elderly Chevy Chase Village resident who has lived in the community for 40 years, "They're great. They always seem to be watchful . . . . They take your newspaper in for you when you're away, or they just might stop sometimes and pet the dogs."

Patrick Murphy, president of the Washington-based Police Foundation and the former police commissioner of New York City, says that no small force can offer all the services and resources of large police departments. But Murphy adds that large police departments can suffer from being too inaccessible and distant from the public.

"The bigger a department gets, the more bureaucratized and over centralized it can get," Murphy said. "The officers are always in cars. They can become strangers to the public. If there is some questionable incident, it is easier for hostility or anger to occur" because the officer is not well known."

For the men who patrol Chevy Chase Village and its 10.4 miles of roads, that has never been the problem.

"We do everything from handling suicides to putting old people to bed," said Woods, 26, the only Chevy Chase officer on duty from 4 to 9:30. "One reason I enjoy working here is that you get a chance to know everybody. I know their names, their dogs' names, and everybody waves."

It isn't unusual for people to stop Woods onthe street just to talk, not to mention waving at almost everybody that passes by. "Sometimes it feels like your arm is going to fall off," Woods says.

In most instances, smaller jurisdictions such as Chevy Chase Village have very little serious crime. There were only 29 burglaries in the area's 702 homes in 1980 and 37 larcenies, according to Chief Burke.

Two of the heaviest activities were traffic tickets (691) and house checks (more than 16,000 in 1980) when residents were away on vacation. The latter is a service county police are unable to provide and often involves checking driveways for strange cars and walking around the back of the house.

In August, at the peak of vacation time, it is not unusual for an officer to have to check 70 to 80 homes during his 10-hour shift, according to Burke.

If something serious does occur, the Chevy Chase Village force can count on the Montgomery police -- and vice versa. Most of Woods' serious calls occur, in fact, when hs is backing up Montgomery police in adjacent beats called "Delta One" and "Edward Four."

"A while back a lot of people didn't like small police forces because they weren't trained and there was very little communication between them and the larger departments," Woods said.

Now, according to Chief Burke, Chevy Chase Village sends its officers to roll call with county policemen, uses the county's police radio network, and passes almost all crimes to the county to investigate.

To become officers, his men have had to pass training at the regular Prince George's or Montgomery County police academies or complete their training in other jurisdictions.

Woods, for example, worked as a Montgomery County deputy sheriff and as a patrolman in Ormond Beach, Fla. He candidly admits that he wound up in Chevy Chase because it was the first local police force to offer him a job. It offered a starting salary of $14,500, which is comparable to most of the Washington area police departments.

Perhaps the most frustrating thing to Woods is that an entire shift can sometimes pass with no significant action.

On this particular day it had been typically tame: helping a man who suffers memory loss find the garage where he left his car, checking homes whose owners are away on vacation, lowering windows on a car so that a black terrier could breathe.

Later on that evening, Woods returned to the home of the elderly woman with the vivid imagination.

"You don't want anything bad to happen, but you've got all this training . . . . F something does happen I just hope that I'm there. . . ."