IN a spare bathroom next to the garage, George Lucas set up his darkroom. He had gotten a 35-millimeter camera about the same time he started high school, and had begun shooting everything from posed portraits of his niece and nephew to trick photos of the family cat, lured into midair by a dangling piece of meat. Before long, he was making backyard war movies on an 8-millimeter handed down by his grandfather.

Anybody who lived near the Lucas place, 14 miles outside of Modesto in California's Central Valley, recognized these ventures as the latest expressions of a quiet boy's creativity. George had already written a weekly newspaper, designed landscapes around his Lionel train set and built a dollhouse for a neighbor girl, scaled right down to a lamp made of a lipstick tube.

Little of this precocity, though, revealed itself in school. A bored, dreamy student, George had struggled with spelling and needed to repeat math the summer after eighth grade. His high school art teacher, looking over George's drawings of space soldiers, admonished him, ''Get serious.'' George's father refused to pay for him to study illustration in college, hoping instead he would take over the family's office-furniture store.

The filmgoing world knows how this particular story ends. George Lucas, the underachieving teenager, grew up to become George Lucas, the phenomenally successful director, auteur of the ''Star Wars'' series, ''Indiana Jones'' and ''American Graffiti.'' Maybe his experience tricking the cat into jumping was an early lesson in how to treat actors.

Except that the story has another prong, far less known, and tied to public policy rather than popular culture....