Some dogs are not a child's best friend.

Lassie, long hair still wet from a heroic plunge into the lake, has earned an undisputed place in cultural myth. But according to a new study Timmy should beware. Though not the worst offenders, collies made the list of biting dogs.

Each year, an estimated 585,000 people suffer dog bites, resulting in about 20 deaths, report Kenneth A. Gershman, now at the Colorado Department of Health in Denver, and his colleagues in the June Pediatrics. Canine assaults account for 0.5 to 1 percent of all visits to emergency rooms. "Dog bites are an underrecognized public health problem," the authors say.

The study of 178 dogs that had bitten someone and 178 dogs that hadn't stresses the importance of prevention and education. "Thirty-seven percent of American households include dogs . . . and yet how many people know the best way to approach a dog is with a closed fist?" asks coauthor Jeffrey J. Sacks of the Centers for Disease Control and Prevention in Atlanta. "These injuries are not accidental. Parents should never leave young children alone with large dogs."

Children under the age of 12 are bitten most frequently -- usually in the facial area - probably because of their size and vulnerability "Dogs attack each other around the head. And the alpha [dominant] dog is always the largest. Young children are usually smaller than large dogs. . . . Also, most children don't have the smarts to recognize dangerous behavior in dogs," Sacks says.

Even so, the risk of bites can be significantly decreased if dog owners make a few simple choices about breed, gender, neutering, and training. The most frequent biters, the study found, were unneutered, male German shepherds and chow chows. These dogs weighed more than 50 pounds, were more than 5 years old, lived in homes with children under the age of 10, spent their days chained in the yard, and had previously snapped at visitors. The study didn't include pit bull terriers: Ownership of this breed has been prohibited in Denver County since 1989. Sacks recommends that animals kept in homes with children not be trained as attack animals.

Breeds less likely to be violent include Chihuahua, golden retriever, Labrador retriever, poodle, Scottish terrier, and Shetland sheepdog, the study shows. Sacks doesn't recommend that parents rush to the pet store to replace their dogs with goldfish or bunnies, but he says they do need to increase their awareness of the risks. "Dogs are a noble species, but we need to recognize they are, after all, carnivores."