Tom Brown Jr. gets twitchy indoors.

Give him a frozen pond to lie on, to observe the wildlife below, or a corner of Central Park to bunk up in, and he'll be happy as a clam at high tide. But put him inside, especially in a city, and he paces, his fingers playing fast octaves on his legs.

At least that's how Tommy Lee Jones portrays the character based on Mr. Brown in ''The Hunted,'' a Paramount film about tracking a fugitive, which opened yesterday. Mr. Brown, who runs the Tracker School in western New Jersey, was the technical adviser for the film, in which the hunter and the hunted set snares, make their own fires and knives, and follow each other based on the tiniest tales told by bent blades of grass.

Mr. Brown, 53, has written more than a dozen books, nearly all of them published by Berkley. In ''The Tracker,'' a memoir that came out in 1978, he recounted camouflaging himself, sneaking up on a badger and petting its stomach. When he is following a person in the wild, he sees more than just lifeless depressions on the ground.

''From one human track, at a glance, I can tell a person's height, their weight, whether they're right- or left-handed, male or female, emotional state, degree of strength, whether their belly is full or empty, what degree of full or empty, and whether they had to go to the bathroom or not,'' he said in a recent interview at his home on this residential area on Long Beach Island, in Ocean County. ''A day before you get any symptoms of a common cold, I'll know.''

To do this, he studies how a foot has hit and left the ground, the depth of a track, its direction and other factors. If you stand on a cool floor, barefoot, and raise your arm or exhale deeply, you can see and feel slight compensatory movements in your feet, he said. These changes, however faint, show up in tracks.

He said that tracks can tell him if a woman is just two weeks pregnant, and he can detect serious health problems among his students. It's a skill he treats with great respect.

''We teach at our school that to scrutinize other students' tracks is a severe violation of privacy,'' he said.

By teaching people how to survive in the woods, he said, he is helping reconnect them to nature.

''When I see a person out on the landscape with a backpack on, that's no better than a scuba diver as far as I'm concerned,'' he said. ''That scuba diver runs out of air, that backpacker loses that umbilical cord, that ball and chain, they're dead. They're aliens to their own planet.''

He said that survival training gives people a kind of insurance policy: ''It gets rid of the apprehension, and you become a child of the earth again. It's no longer wilderness. You're going home.''

While he may not feel at home indoors in cities, he has used his wilderness survival skills on Ellis Island and in Central Park. It is easy to become invisible in New York City, he said.

''I used to have this love affair with the Museum of Natural History,'' he said, ''and I had a hidden scout den across the street in Central Park, so I'd stay there a week, and live in Central Park, eat the plants and live on the ground.''

Warren Moon, executive director of the Wilderness Awareness School in Duvall, Wash., said the most important lessons he gained from the four classes he took with Mr. Brown were about ''awareness, and its connection with aliveness.''

''He's the reason I left my engineering career,'' Mr. Moon said. ''He inspired me to get on the path of helping people foster a connection with the land, which is important for the ultimate stewardship of the earth.''

William Friedkin, who directed ''The Hunted,'' as well as ''The Exorcist'' and ''The French Connection,'' met Mr. Brown 20 years ago. He was impressed by Mr. Brown's ability to find tracks of fox, deer, wildcat and various bird species in the director's Beverly Hills backyard. But then, Mr. Friedkin said, Mr. Brown got down on his living room carpet and accurately described the emotional states of the people who had recently been there.

''He's unique,'' Mr. Friedkin said. ''There's no one else who has his combination of skills and uses them so widely.''

He believed Mr. Brown's stories of tracking murderers and teaching wilderness skills belonged on the big screen.

But Mr. Brown said translating his skills onto film was a challenge. ''Trackers can be hours sometimes for 50 yards,'' he said, ''and it gets boring for moviespeak.''

He learned tracking from Stalking Wolf, an Apache elder whose grandson was Mr. Brown's best friend when he was growing up near Toms River. He has preserved such knowledge in books like his ''Field Guide to City and Suburban Survival'' (1986), ''Field Guide to Nature Observation and Tracking'' (1988) and ''Field Guide to Wild Edible and Medicinal Plants'' (1995).

The movie, which also stars Benicio Del Toro, shows the character based on Mr. Brown training soldiers for the military. This part of his work posed a moral quandary for him.

''I was teaching military escape, evasion, camouflage, the ability to pick out tripwires, thinking this is for guys that are stuck behind enemy lines,'' he said. ''I'm going to make them high-speed, invisible survivalists. I come to find out after several years that they were using these same skills to be more efficient killers. I just stopped teaching after a while for the military.''

He added: ''These skills that are sacred to me were being used just for the opposite. I don't teach to kill.''

The Tracker School, based in Asbury, in Hunterdon County, offers 25 classes, including expert awareness, search and rescue, and intensive tracking. Courses, which often last a week, cost about $800 each.

''The first day, I tell my students take one last look at the ground, because it's the last time you're going to see it this way,'' he said. ''Suddenly it opens up, and eventually they can see a mouse track on a leaf.''