Regarding the opinion-page column "Critical Choice: a New UN Chief," June 10: The implication that an African candidate for UN secretary-general would be a "regional candidate" is both disquieting and outlandish. Is United Nations Secretary-General Javier Perez de Cuellar a representative of South America? Was Dag Hammarskjold a regional candidate from Scandinavia?Africa is just as much a part of the global neighborhood as any other region and a qualified African is just as capable of world leadership as anyone else. The leading African candidates have the experience, vision, and leadership to head up the UN in the 1990s, as it seeks to broaden its mandate and streamline its operations to meet the daunting agenda of the coming decade. Jack Yost, New York, World Association for World Federation Letters are welcome. Only a selection can be published, subject to condensation, and none acknowledged. Please address them to "Readers Write," One Norway St., Boston, MA 02115.