Deputy Minister Easily Wins Tom Fool

''You wouldn't believe what this horse's foot looked like in February,'' the trainer Reynaldo Nobles was saying in the winner's circle at Belmont Park yesterday. ''He only had half a foot. He'd gotten it all infected with a piece of gravel, and we had to cut half his foot out. But it grew back, and he's all recovered from all his physical problems right now. He's the best he's ever been.''

The horse is Deputy Minister, and after the way he won the Tom Fool Handicap yesterday, his trainer seemed justified in also talking about him as a potential horse of the year. Making his first start in five months and carrying top weight of 126 pounds, the once and perhaps future champion ran away from the best sprinters in New York by 4 3/4 lengths. Deputy Minister was the champion 2-year-old in 1981, and he looks ready to vie for titles as champion sprinter and handicap horse as a 4-year-old.

Deputy Minister, who came from next-to-last to circle the field on the turn and draw off handily, returned $8.80 for $2 as the second choice in a field of nine. Fit to Fight nosed out Maudlin and Danebo to finish second, and Copelan finished another 2 1/2 lengths back in sixth place as the 5-to-2 favorite. Deputy Minister went the seven furlongs with Don MacBeth in 1:22 1/5. Suffered Ankle Injury

The Tom Fool was the 12th victory in 16 career starts for Deputy Minister, a Canadian-bred son of Vice Regent and Mint Copy. Originally bred and owned by two Canadian stables, he was purchased as a 3-year-old by Robert Brennan's Due Process Stable. Brennan at first bought a half-interest from the Canadians for a reported $6 million and then bought the rest for an undisclosed price believed to be much lower.

For a long time, it looked like a poor deal. Deputy Minister, who had won eight of his nine starts as a 2-year-old, was the winter-book favorite for the 1982 Kentucky Derby, but lost his first two starts as a 3-year-old and then was sidelined for nine months with an ankle injury. He returned last fall and won an easy allowance race in Canada, but he finished eighth in the Sport Page Handicap.

Then he was turned over to Nobles, who retrained him as a stretchrunner instead of a speedball, and the colt has not lost since. He won the Gulfstream Sprint Championship in his first start this year and then the Donn Handicap at nine furlongs two weeks later. Trainer Is Optimistic