How love for a pet blossomed into love for a family; Duchess, by Chester Aaron. New York: J.B. Lippincott. 182 pp. $10.50. (Ages 12 and older.)

Fourteen-year-old Marty Haliday considers himself one of the coolest kids in New York City. He's head of a gang, whose three members are always in trouble at school or with the police. When a city police dog is lured into traffic, a judge decides Marty should be sent to live with his Uncle Lee, a crusty old California shepherd.

When Marty arrives in San Francisco, he successfully eludes the hired hand sent to meet him. But his uncle soon tracks him down, and Marty is brought to the ranch. Marty soon learns that everyone must work, and if he doesn't work he won't eat.

It isn't until Marty finds a mongrel pup, however, that he begins to feel at home on the ranch. Uncle Lee decides Marty can keep the pup - named Duchess - only if he takes the responsibility for training her properly. As he works with Duchess, Marty gradually learns to demand as much from himself as he does from her.

This is a touching story of a boy who learns to love and care for an animal, and for his family. Although the ending is a bit contrived, Chester Aaron successfully portrays a problem youngster who grows into a caring, responsible young adult.