IN HIGH SCHOOL, we were told by our mathematics teachers that a proof in geometry had to be both necessary and sufficient. The present way we choose sites for hazardous and radioactive wastes in this country, replete with elaborate environmental impact statements and risk analyses, is in some ways necessary. But it isn't sufficient. If it were, we wouldn't have so much trouble finding sites for these locally unwanted land uses--LULUs, in the jargon.