Melanie Smith won the $5,000 Pepsi-Cola Open Junior Speed Stakes tonight at the Baltimore International Jumping Classic on Stillmeadow Farm's Vivaldi.

It was Smith's second victory during the three days of competition at the Civic Center. She won the Open Speed Stakes on the first day riding Calypso, also owned by Stillmeadow Farms.

Smith, 31, of Germantown, Tenn., runner-up in the 1980 World Cup finals here last year, toured the course of twelve jumps without a fault in 44.40 seconds.

Rodney Jenkins of Orange, Va., placed second on Edie Spruance's Second Balcony, in 47.26.

Jenkins, who won Friday night's class on Idle Dice, also took third place tonight on Semi Tough, owned by the Lotus Farm, New Hope, Pa.

Smith is currently in first place in the World Cup standings of North American riders. The 1981 World Cup finals are scheduled for Birmingham, England, April 22-29. However, Smith and the other riders here held a meeting this afternoon and announced their plans to boycott the World Cup.

"Right now the sentiments of the riders are heavily in favor of the boycott," said Robert Ridland, ranked seventh among North American riders.

At issue are financial obligations of the host country. Under international rules the host is to provide transportation expenses for horse and rider and a per diem allowance for riders and grooms.

"They (the organizer in Europe) have come up with some charges that they think are minor, such as import duty," Ridland said. "We sent them a telegram yesterday and they have responded. We are once again going to notify them of our intentions and will discuss our final stand tomorrow after the finals."

Sunday's $25,000 Mercedes Benz Grand Prix is the last chance for North American riders to qualify for the World Cup. Some American riders believe the Europeans do not want the Americans to participate. The United States won the World Cup last year and remains an international power in show jumping.

"It's almost like sour grapes," Ridland said. "They see their domination being taken away. There is an intense resentment. Our bargaining strength lies in the fact that the British have sold tickets based on our appearance. The BBC ratings would go right down."