Melanie Smith on Calypso captured the $25,000 President's Cup Grand Prix last night at the Washington International Horse Show, following a reckless ride around a timed jump-off course against five other finalists at Capital Centre.

Smith, 32, of Germantown, Tenn., riding as a member of the Untied States Equestrian Team, has in the past three years gained a reputation as the one to beat when it comes down to the timed jump-off on the American Grand Prix circuit.

She lived up to that reputation last night before a final-night crowd of 6,500, including Secretary of Transportation Drew Lewis, who presented her the blue ribbon for winning the most prestigious event in the show.

Calypso's victory also justified a recent $500,000 investment made by owner Mark St. James of Windrush Farms of Stonington, Conn., who recently bought the Dutch-bred bay gelding. St. James plans to syndicate him much as is done with race horses.

"It's more fun to own part of a horse as a tax-shelter investment than an apartment," said Smith, who had to abandon riding the horse for three months this summer during the negotiations of the sale.

Smith faultlessly finished the eight-jump course in a time of 32.8 seconds to win the $7,500 first-place money and one of the most important victories on the tour.

Second place went Norman Dello Joio, also riding as a member of the United States Equestrian Team, on Johnny's Pocket, who finished with no faults in 34.1 seconds

"It was one of the hardest jump-offs I've ever done," said Smith, who finished in third place on the Grand Prix circuit last year and now is in fourth place.

"I told Norman (Dello Joio) that the turns were hard," said Smith, who preceded Dello Joio in the jump-off. "I didn't mean to jinx him."