THE TIDE of democracy sweeping Eastern Europe has produced in Yugoslavia a turn from Communism to a particular dark sort of nationalism. The new doctrine is not broadly national but narrowly ethnic, less something that draws people together for an approach to a new day than something that drives them apart on historical lines. This pattern, evident in earlier republic multiparty elections in Yugoslavia, was confirmed on Sunday in Serbia, the country's largest republic and last to go to the polls. Slobodan Milosevic, a former Communist who ran (under a Socialist label) on a platform of Serbian ultra-nationalism, emerged as the clear victor. His Stalinist proclivities alarm many fellow Serbs, not to speak of other Yugoslavs. His rejection of accommodation with the Yugoslav federation's other nationalities invites civil war.

Does it matter to others if Yugoslavia topples back into the ethnic strife traditionally associated with the "Balkans"? The answer is yes. The post-Communist reconstruction of Europe is a fragile enterprise. A breakdown of civility and democratic process in any one part could convulse that part and set a chilling example in others. The disruption potential is evident in that millions of Yugoslavs live outside their home republics, and the republics have tight economic linkages with each other. With civil conflict, great tides of refugees could flow. Yugoslavia's European ties could be broken and Europe's fledgling East-West institutions burdened. The whole notion of a Europe seeking out a common destiny could founder.

In some abstract sense, Yugoslavs have a right to raise the principle of ethnic self-determination above the principle of national accommodation and to sort out their differences by civil war. But in the new Europe this should be regarded as unthinkably selfish, cynical and anachronistic. Other nations should not be sitting around clucking at the awfulness and predictability of it all. They should be using all resources, starting with the brave new all-European political forum called the Conference on Security and Cooperation in Europe, to preempt tragedy. The purpose cannot be to steer the Yugoslavs toward one or another form of federation or confederation -- that's their choice -- but to insist on and guide them to a peaceful and fair pursuit of their future. Yugoslavia has a great deal at stake. The new Europe can't afford to muff this one.