Virtually unknown three years ago, Barclay Tagg's name appears on this season's list of the top 20 race-winning trainers in America. And, although most of the other trainers are ranked because they operate enormous stables, the Marylander has achieved his status because so many of his horses run consistently well.

None of the other top trainers in the country come close to Tagg's 29 percent winning record. And it's no fluke. In 1986, he won with a remarkable 24 percent of the horses he saddled.

Many Maryland racegoers may think of Tagg as an overnight success, but he would laugh -- somewhat bitterly -- at that notion. Tagg has been training horses in the state since 1971; he was little-known because he had so little success. A friend of the trainer puts it more strongly: "Barclay was humiliated for nearly 15 years."

Yet during this whole, frustrating time, Tagg never lost confidence in his own abilities. When he got his first top-class horse, Roo Art, he told the owners to find another trainer because they were second-guessing him and wouldn't let him do things his way. This may have seemed a bit perverse at the time, but Tagg is an uncompromising perfectionist. He is now showing the world what he can do; what he can accomplish with a good-sized stable and a group of owners that has confidence in him.

This is what Tagg envisioned when he came through the gates of Pimlico for the first time in 1971. He had ridden steeplechasers for several years; he had graduated from Penn State; now he was hoping to launch a career as a trainer in rags-to-riches fashion: "I got one filly on the cuff, borrowed a van, drove into the gate and led the filly around till I found an empty stall."

But Maryland in 1971 was a tough spot for a newcomer to break into the business. It was a cliquish place, dominated by a handful of big, powerful stables. It was hard for a trainer to get the all-important allocation of stalls unless he had the right connections. Tagg didn't. Although he had occasional flurries of success, he didn't have enough horses to weather adversity. Like a poker player with too small a bankroll, he kept tapping out. Still, he wouldn't give up. Joe Aitcheson, a fellow horseman with a steeplechase background, kept telling him, "You've got to stay in the game if you want the cards to fall."

It was a long wait. Even after a decade in the sport, Tagg won a total of seven races during all of 1983. But in 1984 he was given six stalls, and he got a promising 2-year-old named Roo Art. "He was all class," the trainer said. "If there ever was a 'look of eagles,' that horse had it."

By the next year, Roo Art had shown enough ability that he figured to be able to take on tougher competition in New York, and his owners were eager to do it. Tagg wanted to give the colt one more easy race in Maryland, and on the day of the race he perceived how unhappy the owners were. "An hour before the race," Tagg recalled, "I told them I'd rather they go somewhere else. I said, 'I'm not comfortable training for you.' I can't work 15 hours a day and lay awake all night."

Roo Art wound up in the care of the country's top trainer, Wayne Lukas, for whom he won major stakes as a 4-year-old. Just about any trainer in Tagg's position should have been demoralized by the experience; entire stables can go into a slump when the "big horse" leaves. Instead, Tagg responded with a phenomenal performance during all of 1986, and has sustained it this year. Although he was always a hard worker, even when he wasn't winning many races, he became obsessive about his work when he saw he was starting to get results.

"This is the only thing I do," Tagg said. "I haven't had a day off since 1984. The whole key to this game is constant attention to little details."

One day last week -- a day when he had started working at 5 a.m. -- he had sent a filly to Delaware Park for a race, and went to his barn to wait for her return. While he was waiting, he busied himself by sweeping behind doors in the barns and pulling down cobwebs. When the filly finally arrived, he fed her and waited until she had finished eating, because the way a horse eats is one of the best barometers of its physical condition. Tagg finally left the barn at 9:30 -- and was back eight hours later.

Tagg's obvious dedication and his mounting success have brought him more owners, and more horses, so that he now has 30 horses in training at the track and another 20 away from the track. But the growing size of his operation has not diluted the quality of his performance. He is effective with diverse types of horses.

Dennis Smoter of Laurel's Sports Palace ran a computer analysis of Tagg's entire 1986-87 record in Maryland. It showed Tagg was most effective in the categories that require the most training skill. When Tagg moved a horse from a sprint into a route race, he won 25 percent of the time. When he gave a horse its first start after a long layoff, he won 28 percent of the time. Even though Tagg has minimal enthusiasm for cheaper horses, he won 26 percent of his starts in claiming races against Maryland's tough, savvy group of claiming specialists.

"Claimers are not my goal," Tagg said. "What I want to do is to train the best-bred horses for nice people." He would like to run a top-class stable -- possibly in a more important racing circuit than Maryland. And he knows what he has to do to reach that goal: to keep on working with the same all-consuming, single-minded passion that has already brought him so far.