In his unblemished six-race career, Cure the Blues has indicated he could be a colt of almost limitless potential. But he has evoked considerable skepticism, too, because he never has had to face a serious challenge, never met rivals of quality.

Sunday afternoon, the questions about Cure the Blues ought to be answered unequivocally. The one-mile Gotham Stakes at Aqueduct will be a genuine test of him; so genuine, in fact, that it is possible he will be beaten. Even trounced.

His competition will come from Proud Appeal and Noble Nashua, 3-year-olds who have won brilliantly in New York this season, running faster than Cure the Blues ever has in his life. And they will be delivering a one-two punch at the favorite. Proud Appeal probably will run head and head with Cure the Blues, while Noble Nashua stalks both and waits for them to falter.

Last fall, when he concluded his brief but perfect 2-year-old season, it seemed inconceivable that any member of his generation could challenge Cure the Blues in a one-mile race. He had won his five races by a total of 38 1/2 lengths and had never been headed. Only the limits of his stamina figured to stop him.

But problems with his foot delayed the start of his 3-year-old season, and when he did return to competition at Hialeah last week he did not win impressively, even though the seven-furlong distance should have been optimal for him. He had trouble at the start of the race, and after getting the lead he didn't move away from his mediocre rivals with any explosive burst of speed.

This, in truth, was a minority view held by The Washington Post's observer and by virtually nobody else at Hialeah that day. Most everyone shares the assessment of trainer LeRoy Jolley, who said, "His race was very, very big. He overcame a couple of serious obstacles. He lost his shoe and stumbled badly at the start, but he still got up and won very easily. He's a very, very nice horse."

Even if this interpretation of Cure the Blues' performance is correct, and he is ready to run a blockbuster race Sunday, he still is no cinch to beat Proud Appeal and Noble Nashua in the Gotham.

Noble Nashua lost to Cure the Blues by 14 lengths last fall, but he was an inexperienced runner at the time and he has blossomed this year. Five weeks ago, he won a minor stake at Aqueduct by nine lengths in a time that had speed handicappers staring at their figures in disbelief. It was the sort of performance that wins Derbies and championships, and if it wasn't a one-shot phenomenon, Noble Nashua will be a prominent name for the rest of the racing season.

Proud Appeal's credentials still are a bit suspect because he never has run farther than seven-eights of a mile, but he has done little wrong up to this point. He has won five of his six career starts, most recently the Bay Shore Stakes at Aqueduct. He ran seven furlongs in a sensational 1:22 1/5 over a dull racing surface, and even Jolley conceded, "It was a super race."

If Proud Appeal can maintain that level of performance in longer races he, too, has the potential to become a champion. The Gotham will test his legitimacy as a Derby contender just as it will test Cure the Blues.