An enviornmental group on Thursday asked the European Economic Community to ban exports of toxic wastes to the Third World. Greenpeace claimed such exports have boomed over the past year because international regulations are too lenient. Ernst Klatte, the group's spokesman, called for the ban at a news conference in Luxembourg, were a meeting of European Economic Community environment ministers was being held. Greenpeace cited recent exports of toxic wastes from Europe and the United States to Africa and from the United States to Latin America and the Caribbean.