The metropolitan area's startling rise in crime in recent months has prompted many residents to invest considerable time and money to protect themselves and their belongings. Many people react to crime by installing bars on windows or a burglar alarm system. For many others, protection means a dog.

"Having a dog in the house really is a deterrent to burglars," says Det. Thomas Gentry of the D.C. Police burglary unit. "The majority of homes broken into don't have dogs. Often a burglar will be scared away by a dog in the house."

But too many people, intent on rushing out to buy a four-legged bodyguard, forget, says Phyllis Wright of the Humane Society of the U.S., that they are bringing home a living, breathing creature requiring proper care and attention.

"Basically, a lot of people don't understand what they're getting into," she says. "A dog is good protection, but it's not a computer that works when you press the right buttons.Before you get a dog for protection, you better think about whether you really want a dog."

Wright cautions that if you don't have a fenced yard, getting a dog for protection may actually put you in danger, because it means you will be out on the streets walking the dog at night when you would otherwise be safe in your house.

The common perception of the so-called "guard dog" is of a German shepherd or Doberman pinscher, complete with spiked collar and a fierce growl. There's logic behind that perception -- both Dobermans and German shepherds have been bred for their protective instincts as well as for their aggressiveness. But will Fang the Doberman be more of a deterrent to a burglar than Sam the mutt? Probably not.

"It doesn't really matter what kind of dog you get," says Gentry, "as long as it has a big bark." Many burglars are not worried about being attacked by a dog as much as they are afraid a yapping dog will alert a neighbor to call the police. Gentry also points out that if a burglar has cased the house thoroughly in advance, he will probably come prepared to quiet the dog with Mace or chloroform.

Basically there are three of what Wright calls "protection dogs": alert dogs, guard dogs and attack dogs. Remember that any dogs you get for protection must live in the house with you. Chained to a doghouse in the backyard, even the scariest looking dog doesn't offer much protection.

An alert dog is any dog that barks to warn you when someone rolls into your driveway, knocks on your door or wanders onto your property. Of course, the dog doesn't know the difference between a burglar and your Aunt Martha. If you encourage it to bark, you'll also have to live with the consequences (which may include violations of noise ordinances in some areas). Nevertheless, Wright and Gentry agree that alert dogs provide more than adequate protection for the average homeowner.

A guard dog usually is a larger dog that has been trained, either by you or a professional, to protect you and to take positive action toward any aggression. Not surprisingly, guard dogs of any breed are more likely to bite than are dogs whose natural aggressiveness has not been reinforced.

An attack dog is an animal that has been trained to attack on command. Wright, who has trained attack and sentry dogs for the Army, says only specially trained police and military personnel should have attack dogs. Usually trained and handled exclusively by one person, attack dogs can be extremely dangerous in a home or community situation.

"I would never own an attack dog," Wright says. "Having an improperly trained attack dog is like keeping a loaded gun on your dining room table. Once that dog attacks, there's practically no chance of recalling it."

No matter what type of protective dog you choose, it's important to remember that every dog has the same basic needs. Dogs need to be housed, fed, and to have proper veterinary care. They also need exercise, companionship and supervision, especially during puppyhood.

If you're thinking of getting an alert dog, Wright recommends what she calls the "feisty breeds." Schnauzers and terriers are small to medium-sized dogs that make good family pets, yet are sensitive to their surroundings. All dogs have sharper hearing than do humans, but a terrier's hearing is particularly acute.

Wright says that when something is going on around her house, it's the terrier who notices first and alerts the Doberman.

Sporting dogs (retrievers, setters and spaniels) are not as good choices for alert dogs, since they have been bred over the years to remain calm under aggressive circumstances.

If you're seriously considering a guard dog, you almost have to begin with a puppy, says Wright. A guard dog is trained to protect you and you alone, which can be risky if you live with others.

The first step is to find a reliable breeder. Make sure you meet the dog's parents and you check the breeder's reputation. A guard dog doesn't have to be a Doberman or a German shepherd, but most of them are.

The single most important part of a guard dog's training is basic obedience.

Obedience training should start at 6 months of age. Guard training, which should not begin until the dog is at least a year old, consists mainly of reinforcing the animal's natural aggressive tendencies rather than training it to become vicious. Wright firmly believes that all training should be done by the owner, with professional guidance.

A few words of caution: Don't leave a guard dog unsupervised, especially around children. Children's roughhousing is all too frequently mistaken for real aggression. In fact, if you have children you probably shouldn't have a guard dog.

If you keep in mind all of the responsibilities that accompany dog ownership and are willing to accept them, a dog can provide protection as well as companionship. If nothing else, a dog is certainly more affectionate than a burglar alarm.