Of the five best 3-year-olds in America, all but one fit the standard profile of a Kentucky Derby horse. All but one have expensive bloodlines, come from fashionable New York stables and are trained by men who are accustomed to handling champion racehorses.

The one exception to this profile is Roo Art, and maybe that is the reason nobody outside of Maryland thinks of him as a contender for the Kentucky Derby. After all, he did start his career in a $20,000 claiming race and he is trained by Barclay Tagg, who never has managed a top-class horse before.

But Maryland racing fans who have seen him run know that Roo Art belongs in the company of colts like Proud Truth, Chief's Crown, Rhoman Rule and Stephan's Odyssey -- the acknowledged leaders of this generation. Tagg is not completely convinced, but he knows it is reasonable to plan a campaign for his colt that may lead to Churchill Downs.

This is what every trainer dreams of, but the chances would have been considered remote that one of the country's best 3-year-olds would be found in Tagg's barn. In 14 years as a trainer, he has never had a top stakes horse; in many of those years, his total victories did not reach double figures.

Tagg graduated from Penn State in 1961, became a steeplechase jockey for a while, and then set out to become a trainer. He worked for a year as an assistant to the legendary Frank Whiteley, then launched a career that could not be described as meteoric.

Tagg is respected in Maryland as a smart, conscientious horseman, but he rarely has had high-quality stock to train. Some trainers get to spend seven-digit sums for their clients at yearling sales. When Tagg last year got new clients, Barbara and Bert Holleran of York, Pa., they said they wanted a horse for about $15,000.

Tagg obliged, and at a sale of 2-year-olds in training at Timonium last May he spent $15,500 for the colt who might change his life.

Roo Art made his first start in a maiden-claiming race at Laurel and won it by a dozen lengths, then scored two more victories before taking on King Leatherbury's unbeaten I Am the Game in the General George Stakes last month.

When Roo Art stumbled badly at the start, he looked as if he might have conceded his rival an insuperable advantage. But he came from 10 lengths behind, swooped around the field and scored a decisive win that let Tagg know that it wasn't foolish to start thinking about the 3-year-old classics.

After his stint with Whiteley, whose adversion to the Derby is well-known, Tagg knew all the drawbacks about rushing a colt to get ready to go 1 1/4 miles so early in his career.

"I know the arguments against it, and I know there are a lot of nice colts around this year," he said, "but Roo Art has a super disposition, and distance and weight don't seem to bother him. Those are definitely big factors on the first Saturday in May."

Tagg sent Roo Art to New York last week for an allowance race in which he finished third, but the loss did not tarnish his credentials much. He tried to come from a distant last against a formidable speed horse, Nordance, who was loose on the lead, and the time of the race was excellent -- better than many of this season's big stakes races for 3-year-olds.

Tagg will probably ask Roo Art to make his next start in the Cherry Hill Mile at Garden State April 6 (although he is also considering the rich Jim Beam Spiral Stakes at Latonia). Then he would go in the 1 1/8-mile Garden State Stakes. From there, if he runs well, he would go to Churchill Downs.

This quest will be every bit as tough a challenge for the trainer as for the horse. Nothing in the profession offers so much pressure, so many pitfalls. Another Marylander, Dean Gaudet, thought she could handle the challenge when she took her good colt Mighty Appealing to Florida this winter, but she wilted under the pressure and may have ruined the horse.

Tagg isn't fazed. "I'm friends with John Veitch, David Whiteley and Billy Turner; I've seen them all do it. To tell you the truth, I don't feel much pressure at all. We do a lot of work on our horses; we give them a lot of attention; we do our homework. I feel I'm capable."