On the spring day in 1976 that she climbed aboard a horse named Cione at Pimlico, Karin Yarosh was the most promising female rider in Maryland.

Unlike so many other women who were ill-equipped to break into a male-dominated profession, Yarosh was strong, aggressive and utterly fearless. She would regularly drive her mounts through narrow openings along the rail where more prudent riders would fear to tread. But this virtue proved to be her undoing.

Cione was racing in the middle of the pack, no more than a foot from the rail, when another horse moved abreast of him, angled slightly toward the inside, bumped him and knocked him off stride The next few seconds started an ordeal for Karin Yarosh that has lasted for the past 2 1/2 years and may never end.

"My horse swerved and hit the rail and went to his knees," she recalled yesterday. "I flew over his head. I was lying on the track, by the rail, and the only thing I could think was to roll under the rail."

With several half-ton animals bearing down on her, Yarosh desperately tried to scramble to safety. She did not make it. Suddenly, she said, "I felt so much pain shooting through my body I couldn't believe it. I knew I was hurt bad."

The doctors at Sinai Hospital knew it, too, when they undressed their patient and saw a vivid imprint of a horseshoe on her side. In surgery they worked on Yarosh's punctured lung and broken ribs, and removed her gall bladder and two-thirds of her liver.

Yarosh spent the next four months in the hospital, but when she went home the doctors told her she would probably be able to resume riding in a year. That was all she wanted. Yarosh had started galloping thoroughbreds when she was 16 while she worked on a farm near her home in Port Deposit, Md.

When she came to the track she spent 3 1/2 years galloping horses and working in the stables before she got the chance to ride in actual competition.

Having invested so much time and energy in her preparations to become a rider, Yarosh deserved more of a return on the investment than the 28 races she won before the accident. But she did not get it.

Two months after she was released from the hospital her skin started turning yellow. Doctors said the liver was still not functioning properly and she would have to undergo surgery again. After eight hours on the operating table, Yarosh woke up and heard the doctor tell her: It didn't work.

"The bile ducts in the liver had been destroyed," Yarosh said, "and the doctor at Johns Hopkins is trying to make me new ones. It's worked so far: it's kept me alive. Now I've got a tube running through my liver and out my side. They're supposed to take it out next month, and the doctor has told me there's a 50-50 chance the whole liver will collapse."

On top of all the worries generated by her physical problems, Yarosh feels abandoned by her former colleagues.

"When I joined the Jockeys' Guild," she said, "I felt that no matter what happened I'd be taken care of. I'd been getting compensation from the Guild, but they cut down the money and now they're cutting it off. I went to the track and talked to Bill Passmore, the head of the Guild, and told him I still had to buy a lot of medicine, but he just shrugged his shoulders and said, 'Karin, I can't help you.' I think if I'd been a guy that wouldn't happen."

Yarosh never asked for deference from male jockeys, or anybody else, when she was riding. She made her way into the profession with determination and perseverance. But now she finds herself in a situation where those qualities cannot help her.

All she can do is wait passively for the outcome of the complicated medical procedures being performed on her. Wait, and hope, and dream of returning to the track.

Yarosh recently took and passed a test to get a Maryland trainer's license, though she does not have any immediate prospects of getting a stable of horses to train. But what she most wants to do is to ride again.

"I kind of wish that after the accident I'd feel scared to death," she said. "But I love riding and I miss it a lot. I've done a little pleasure riding on a horse who's very gentle, but the doctor says that's all I'd better do because if I fell again the whole liver could rupture. If I were well, though, I'd be out there riding the way I did before."

That, she knows, is a dream that will probably never come true.