A hundred years ago, judges were locking up cattle rustlers. Now leaf rustlers are criminals.

Heidi Prescott, national outreach director for the Fund for Animals, served a maximum 15-day sentence in a Maryland jail (with two days off for good behavior) for rustling leaves with her feet in a public wildlife management area. She was in the woodland on Nov. 25, 1989, the opening of the deer-slaughtering season, when some of Maryland's toughest hombres were displaying their bravery by pumping bullets into the brains and hearts of does and bucks.

Prescott, an idealist who believes in the sacredness of all life -- four-footed as well as two-footed -- was arrested with a group of others for breaking a state law that forbids harassing hunters. For the harassment of rustling leaves, as well as talking to the gunners as they hied into the woods to risk life and limb -- the deer's -- Prescott was fined $500. She refused to pay. The judge, aiming his judicial gun at this menacing target, sent her off in handcuffs for contempt of court.

Having never met a criminal leaf rustler, I went to the county jail -- a maximum-security operation -- to talk with Prescott. She is 28, a graduate of Pennsylvania's Edinboro State College and the daughter of a Methodist minister who is now a counselor. She smiled broadly when mentioning that after seven months with the Fund for Animals, and a fair number of 80-hour weeks, she won a raise from $12,000 to $14,000. She believes that the simple life is the good life is the humane life, and if we can't end the war against animals chances are slim that we can stop the wars against each other.

Although terrified the first night in jail, Prescott was calmed by the warmth shown her by fellow prisoners. She was a curiosity -- a jailbird who chose deliberately to fly into the coop. ''This is an odd place to have my faith in human nature restored,'' she said, ''but that's what has happened. Not one person has criticized me for what I did on behalf of the animals that day. No one has said, why don't you fight for a more important cause, which is what I hear all the time on the outside.''

Prescott, a vegetarian whose diet includes no dairy products, went on an unofficial hunger strike the first few days in jail. She wouldn't eat the meat or animal-related food. When vegetables were served, she would trade her meat with others. After a week, she successfully challenged the jail's dietary rules, which sanction vegetarian meals for only religious or health reasons. She broadened it to a third category -- ethics.

In the five years between college and the Fund for Animals, Prescott served society as a wildlife rehabilitator. It was volunteer work, rescuing animals hit by cars or wounded by hunters, nursing and then freeing them back into the wild. ''I suppose I saved about 100 animals a year,'' Prescott estimated. ''Most were squirrels. I learned a lot about the innate struggle for life that each animal has. I'd come on a near-starving animal or one half-dead after being hit on the road, and I witnessed the intense fight to stay alive. You learn from those kinds of experiences how all life should be cherished.''

When not bottle-feeding infant squirrels -- every two hours everyday for as long as nine weeks -- Prescott earned a small living from artwork. One of her largest paintings -- 30 feet by 4 feet -- was sold to the Brookings Institution in Washington for $6,000.

In the tradition of pure civil disobedience, Prescott accepted her jailing but not the reasons for it. She told the court, ''I remain convinced that my behavior was appropriate. I did not physically strike, obstruct, yell at or insult any of the hunters with whom I communicated. I simply exercised my First Amendment right to voice my objections to the cruelties of sport hunting and my right to walk on public lands.''

U.S. jails are packed with people guilty of violent crimes. Prescott may be one of the first people in U.S. history jailed for trying to prevent violence. She sees her imprisonment as a positive, not a negative, experience. ''They look on my being here as a punishment. I don't. I see it as a chance to grow, a time in which my beliefs are being tested and strengthened.''

Prescott, along with growing numbers of citizens who think public wildlife lands are for animals, not their slaughterers, see this arrest and jailing as the beginning of a nonviolent protest movement, not its squashing. Prescott is a crime-fighter, with one message for woodland gunmen: Take a hike, boys.