BRUSSELS in April and June is rocked by riots of ethnic Arabs complaining of no work and mistreatment. In Norway, a shopkeeper tells one reporter he still hates Germans for their occupation during World War II - but today he worries more about the influence of ethnic "Norwegian Muslims."Across Europe new ethnic groups are stirring. Moreover, the possibility of a huge increase of immigrants or refugees from countries surrounding Europe - from the exploding populations in North Africa to the economically unstable regions of Eastern Europe and the Soviet Union - worries both the publics and politicians of Western Europe. This isn't exactly what the architects of a "New Europe a coordinated and consolidated economic trading bloc beginning in 1992 - planned on. Europe '92 is the biggest structural change on the continent since the rise of the nation-state in the late 19th century. But the well-laid plans of Europe '92 did not include the messy problems of ethnicity and cultural clashes. Nor, for that matter, did they anticipate the end of the cold war - with its resulting rise of nationalist feelings in the old East bloc, apparent today in Hungary, Romania, and especially Yugoslavia. The spread of immigrants and refugees intensifies deep-seated political, social, and cultural issues in Europe. It threatens to tear the fabric of the EC. How do European nations retain their sense of identity and security and still accommodate new groups? Can centuries-old prejudices and fears - historic patterns of provincialism - be overcome? Shouldn't liberal democracies acting in concert provide a reasonable transition and education for new groups? On the other hand, should European nations be expected to unquestioningly open their doors to outsiders? Populations usually move en masse because of failure and instability at home. Must a France or a Germany inherit these problems? Italy and France have 10 percent unemployment. Spain, 15 percent. Western Europe is not the kind of undeveloped, open land - the social "safety valve America was in earlier periods. A debate on immigration policy - what the rights of new groups are, and how to differentiate between refugees and immigrants - is needed. A sensible policy must emerge. It will not be helpful to shape the debate as a question of xenophobic right-wingers versus enlightened and tolerant democrats. That's too simplistic for the major cultural changes under way.