If Flag Admiral wins the Preakness, they may play "Hail to the Chief" in addition to "Maryland, My Maryland" at Pimlico.

Former president Jimmy Carter has bought an interest in the promising 3-year-old colt, after seeing him win an allowance race on the day of the Kentucky Derby.

Carter had been a guest of Tom Gentry, the flamboyant Lexington breeder who owns Flag Admiral. Before the colt was supposed to run in the fourth race at Churchill Downs, Gentry learned that his scheduled rider was not available. "Mr. President," he said, "you act as my trainer. I've got to get a rider."

The two of them went to the jockeys' room, where Carter was introduced to a number of the jockeys. Gentry made one of the introductions: "Mr. President, right here is a very good jockey, Jorge Velasquez, who is riding the favorite in the Derby."

Carter said, "Jorge, how would you like to ride my horse?"

"Are you kidding?" the jockey exclaimed, and quickly changed into Gentry's blue-and-yellow silks.

In the paddock, Gentry prompted Carter before he gave Velasquez his instructions. "Tell him to take a long hold, like he was going two miles," Gentry advised, "and to let him out turning for home." After conversing with Velasquez in Spanish, Carter gave him those instructions and added, "Jorge, you'll win."

Amy Carter watched with skepticism. "I wish Dad wouldn't do that," she said. "What if he gets beat?"

That, of course, was a distinct possibility; Flag Admiral was only the second choice in the wagering. But Velasquez took a long hold, advanced on the rail, asked the colt for a response turning for home and drew away to a smashing 7 1/2-length victory, covering a mile in 1:35 2/5.

Carter turned to his wife, Rosalyn, and said: "I gave the orders!" Their entourage headed for the winner's circle and, Gentry said, "He got a hell of a charge out of it. You would have thought he owned him!"

In the days following the Derby, Gentry discussed the possibility of Carter's buying a piece of Flag Admiral with their mutual friend, Dale Sights, who was Kentucky chairman of Carter's campaign in 1976 and now is a member of that state's racing commission. Neither Sights nor Gentry would disclose what percentage of the colt Carter bought.

Flag Admiral has the ability to generate a quick return on the investment. The son of Hoist the Flag ran dismally in his first three starts, but broke his maiden impressively in an allowance race at Keeneland last month, then ran away with the allowance race at Churchill.

His lifetime earnings, however, are only $17,495, the lowest of all the Preakness candidates. If more than 14 horses are entered in Saturday's race, he would be excluded, and would probably run, instead, in a lesser event for 3-year-olds on the same day's program.