There is a chart of horse breeds on the door of Jennifer Landau's bedroom. Around her bed are pictures of horses. Hanging on a string and jumbled on a shelf are at least 50 ribbons and horse show trophies. Her collection of more than 100 plastic and metal model horses takes up a whole bookcase. Some are eight inches high, some are only one inch high.

Across the room are the glass horses, dozens of them, that she picked up in Greece, Italy, Mexico and other places around the world. Instead of a dollhouse, she has a model stable that someone gave her when she was 10. The mobile dreamily swaying in the air is a mobile of horses. There is a picture of a horse on her blouse.

Jennifer is 14. She like horses.

"I've only seen 'The Black Stallion' twice," she apologizes. "I plan to see it a hundred times. I read all the books, of course."

There are 26 of them in the series written by Walter Farley. She has also read the James Herriot books about a veterinarian and the Will James books about a cowpoke. "The Black Stallion" is about a young boy, but the folk wisdom is that, as a rule, horses happen to girls.

What is it about horses and girls? There are more theories than you want to hear. Boys have school sports to keep them interested, you'll be told, or they get involved with model planes, or they discover cars. Someone else will insist that with girls under 16 or so, horses are a substitute for boys, who are generally impossible at that age. And there is the social thing: It's chic. For some, a horse show is a place to meet horsey people.

That doesn't sound like Jenny at all. With her, it just happened.

"I started when I was 9. A friend got me interested, Jill Schachner. I spent a lot of time with her and rode her horse, and finally I got a tiny pony. But she was so fat she wouldn't do a thing."

Her parents, thinking that a horse would be a great idea for giving her self-confidence and a sense of responsibility, leased a larger pony, a white gelding named Frosty.

Her father is Dr. Stuart Landau, an ear, nose and throat specialist, and her mother, Judith, works at the Hirshhorn. Their house, in a suburban forest off River Road, is full of modern sculpture.

"I had him a year-and-a-half, but then I outgrew him too, and I needed a bigger one. That's how I got Prinny. Her name is J. A. Princess. How we met was a fluke. I was out of school and I went with my Mom to her office, and in this other lady's office was a picture on the wall. I said, 'Oh my God, I need a pony just like that one,' and she said, 'Well, my daughter just outgrew her.' I said to my Mom, that's the pony for me."

She went out to see the pony, rode her and talked to her.

"From that day on, I loved her," she says, simply.

"She knows the car. She comes running up when I call her. Always looking for an apple. I don't give her sugar. I'll never sell her."

But, she adds, she might lease her out if she outgrows her.

(To some of us farm kids, the notion of outgrowing a horse, like a bicycle, seems a bit exotic. To us, a horse was a horse, whether it was old Charlie, big as a Percheron, who could take three of us at the same time with our legs sticking straight out from his broad back, or a preposterously neurotic oversized pony named Baron who would buck at the shadow of a single leaf. But that was a long time ago.)

Horses are not a hobby for everyone. They can run you from $1,000 to $3,000 or, of course, if you want something special anywhere up to half a million.

Then's there's the tack. A saddle costs $700, and you add the bridle and bit and other odds and ends, and the $25 for trailering the horse to a show, plus $4 entry fees for each event. And stabling: Prinny is kept at the Evans Stable, at $125 a month plus grain, out past Potomac on River Road.

"Mom pays for that, but I pay for half the upkeep. I get an allowance, and I baby-sit. Last weekend I earned $20 baby-sitting, and that goes in the pot. You're always buying new things. Boots are $100 or so, which is kind of rough if you're still growing."

At the stable, Princess is fed and her stall is cleaned, and if the Landaus go away on vacation Jenny's friends will exercise her, just as she will ride their horses when they're away. But the responsibility is Jenny's.

"I took courses at the Potomac Pony Club," she says. "I know, when a horse looks sick, what the symptoms are. I know what to do. The stable gets the shoe man for you, but you have to know when."

Most afternoons after school -- she's in the ninth grade at Tilden Junior High -- she goes to the stable and stays till closing time.Weekends she is there all day long. Often she gallops the sleek bay for a mile over the hilly pasture by the stable. Sometimes she rides up the towpath to Great Falls or jumps the horse in the ring.

On this particular Saturday, the sky was trying to snow, and it made Princess a little wild. Jenny had been working on her, scraping the dirt from her hooves with a special scraper from the box of brushes, currycombs, leather oils and other horse cosmetics.

Several other girls in their early teens were in the stable too, puttering around their horses with the same timeless absorption.

"Prinny has days when you can't control her. The wind makes 'em frisky. They just don't care. We do a lot of cross-country and dressage, and I try to show her every month. She's very willing and never scared. Always willing to try something, but if your scared, she won't."

The night before, she had spent hours cleaning the bridle. Because of the cold, she had covered Prinny with a blanket, but the pony didn't like it.

"She's mad at me. She bit her nameplate."

That would be the carved nameplate Jenny gave her on their first anniversay last June. She also made a carrot cake for the occasion. (That's nothing. Some girls keep locks of hair from all their horses. Some girls habitually hold telephone books between their knees to strengthen their legs.)

Now they are walking out to the ring. It is their first ride in two weeks because Jenny had the flu. She talks to the horse like a best friend.

"Oh you brat," she mutters stroking the long brown neck. She wears brown suede chaps over her jeans. Her name is written on a small metal plate tacked to the saddle. With some effort she scrambles aboard, and then she's off in a stiff little canter around the ring. Soon the pace lengthens to a more relaxed stride.

"She doesn't get fuzzy in the winter. That's because she's a thoroughbred.

She's part Welsh thoroughbred."

Some of the other girls are riding now. One is still trying to catch her horse. Jenny loses a stirrup but keeps her seat. She has been known to fall, and one time even took a spill at a show, only to find that her boyfriend had taken a snapshot of this awkward moment. The picture is in her horse scrapbook.

Jenny hopes to work at a racetrack this summer, if her father can arrange it. He rides a bit too. Her younger brother would rather play soccer.

In any case, Princess is very much a member of the family.

"I'm her chauffeur," says Judith Landau. "I'm a horse show mother. But I get a lot of pleasure out of the way Jenny takes responsibility. And we've shared some good times. All those mornings when we were going off to some horse show. Braiding the mane in the dawn . . . ."

They have left the ring now, the girl and her horse, and in a minute they will head for the pasture. They are standing there on the dirt road thinking of something else, and the girl's hand reaches up along the pony's soft jowl, an automatic gesture of possession and love. The pony's delicate nose brushes the girl's sweater, nuzzling with a little upward thrust. It is exactly the same kind of gesture.