When Melanie Smith and Calypso landed over the last of seven fences in the timed jumpoff of the $25,000 Mercedes-Benz Grand Prix, the crowd of 7,200 in the Civic Center this afternoon gave them a standing ovation.

"They should never let her go last," said Michael Matz, who placed second on Jet Run. Smith was the final rider of eight to jump off in the final 1981 North American World Cup Series. She finished in 25:95 seconds. "I think she's crazy to go that fast," added Matz, who preceded Smith in the jumpoff and clocked 27:55 seconds.

Smith, 31, of Germantown, Tenn., reaffirmed her first-place domination in the World Cup standings of U.S. riders. She will lead the North American contingent competing in the 1981 finals, scheduled for Birmingham, England, April 22-29.

During the three days of international competition here, continual transatlantic negotiations went on between the U.S. riders and European World Cup organizers over the financial obligations of the host country. At last, a telegram from Europe late today announced that all the money necessary for the championship was available.

"They have already paid the $150,000 air fare for the horses. The plane is ready and so are we," said Matz, 30, of Plymouth Meeting, Pa.

On Saturday, the U.S. riders had announced their intention to boycott. "It was almost sour grapes," said Robert Ridland, one of the riders on the tour. "They (the Europeans) have completely dominated the sport for so long that when the U.S. started to win two years ago, they didn't know what to do."

The opportunity to win the one prize that eluded her last year had Smith beaming. During the 1980 finals here, Smith was edged by Conrad Homfeld, putting her in second place. Already the leading woman rider, and rider of the year in 1978, she said the World Cup "would be very nice to win. The time seems right. My horse is young and competitve in Europe is the best."