United Nations, N.Y. — Costa Rica has decided to withdraw its candidacy for the vacant UN Security Council seat and Panama's election now seems certain, said an authoritative source. Panama jumped ahead in the latest round of voting for the vacant seat, receiving 93 votes against Costa Rica's 52. A country must have 97 to be elected. Panama's decision to enter the race for the vacant Latin American Seat came after the election of Ronald Reagan, a bitter opponent of the Panama Canal treaties ceding US control of the waterway to Panama by the year 2000. As a Security Council member in 1976-77, Pa nama frequently used the Council as a forum to press its claims to the canal.