UNITED NATIONS, N.Y. — A SMALL advance team of United Nations military observers from Ghana, Singapore, Kenya, and elsewhere is slated to arrive in Belgrade Dec. 18. The 21 observers are to fan out into four areas of the toughest fighting - in what some diplomats call the "ink blot" approach - to assess the prospects for sending in UN peacekeepers.This advance contingent will be led by Herbert Okun, former US deputy representative to the UN, who has just completed four diplomatic missions to Yugoslavia as special adviser to Cyrus Vance, a UN envoy. Mr. Vance insists that any UN peacekeeping venture - the first on European soil - must be preceded by a lasting cease-fire. So far he has given no green light. "Peacekeeping is not a peaceful business - I would urge caution," says Augustus Norton, professor of political science at the US Military Academy. "When UN forces are put in the midst of an environment where it's not quite clear that the belligerents want them to succeed, then that's a recipe for disaster. It's what happened in South Lebanon." Even as it searched for ways to support European Community (EC) efforts to resolve the conflict, the UN was caught up in the ongoing dispute over whether prompt diplomatic recognition of Croatia and Slovenia would help or hinder the peace process. Germany has long made it clear - most recently in a lively weekend exchange of letters between German Foreign Minister Hans-Dietrich Genscher and UN Secretary-General Javier Perez de Cuellar - that it intends to recognize the republics and that it views any other approach as "dangerous." Until recently, France, Britain, the US, and Mr. Perez de Cuellar opposed recognition prior to a political settlement. France and Britain pushed tough wording in a draft Council resolution, warning nations against action political or otherwise that might inhibit a cease-fire or the peace process. In a round clearly won by Germany, the "political" reference was dropped. Then on Dec. 17, EC foreign ministers said they would recognize breakaway Yugoslav republics on Jan. 15 if they complied with a checklist of good conduct. Conditions, which Germany says will not affect its decision to recognize Croatia on Dec. 19, include guarantees for minorities, human rights, and a respect for borders. Many observers now agree that Yugoslavia's days as a united country are over, and that the Serbs - who have had the upper military hand - are the aggressors. David Calleo, director of European Studies at the Johns Hopkins School of Advanced International Studies in Washington, suggests that where there is no will by the parties to settle a conflict and no desire by the UN or Europeans to intervene militarily, current efforts could amount to no more than a "bureaucratic merry-go-round." "As long as one side thinks it can win and nothing can stop it, what good are UN observers?" he asks.