Nelson Mandela's grand and glorious reception in New York City came about only after some backstage scrambling. The problem? To avert major protests by Jewish organizations upset at Mandela's tendency to equate the black South African struggle with that of Palestinians and at his warm words for Arafat. Before the scheduled visit, Harry Belafonte and Roger Wilkins, officials of the Mandela welcome committee, arranged for Jewish leaders to meet with Mandela in Geneva. Though he succeeded in mollifying some of them by acknowledging Israel's right to exist, more militant Jews went away from the talks still intent on staging protests during his visit because of his insistence that Israel should return to its pre-1967 borders. What finally assured the harmony that prevailed for nearly three days was an unpublicized phone call from another rebel who, like Mandela, knows how it feels to be a prisoner of conscience: Natan Sharansky, the freed Soviet dissident who now lives in Israel.