Shultiz on Boycott

"Secretary of State George Shultz, responding to critics who say U.S. policy toward South Africa perpetuates apartheid, said Tuesday the United States ''must not throw American matches on the emotional tinder of the region.''   Shultz, speaking at a National Press Club luncheon, expressed sharp opposition to a proposal before Congress that would ban new U.S. investment and reduce U.S.-South African trade ties.   He said the proposal ignores the harm that would be inflicted ''precisely on the black majority whom the advocates of boycotts, embargoes and sanctions purportedly want to help. "