SOUTH AFRICAN POLICE in Pretoria fired tear gas Tuesday to break up a march by hundreds of neo-Nazis demanding the release of an imprisoned white extremist on a hunger strike . . . RADIATION LEAKED from a Japanese nuclear waste safety testing facility, marking the country's third nuclear accident this month and raising concern over the government's atomic energy safety policy, experts said. The accident at Tokai Mura northeast of Tokyo took place Saturday but was not revealed until Wednesday.