BONN — GERMAN Foreign Minister Hans-Dietrich Genscher said yesterday Bonn would recognize Yugoslavia's breakaway republics of Croatia and Slovenia as independent, despite warnings from Britain, the United States, and United Nations Secretary-General Javier Perez de Cuellar that this could block peace efforts.Mr. Genscher said he believed the rebel republics would meet standards for recognition that Germany and France would propose to European Community (EC) foreign ministers in Brussels today. Yugoslav officials in Belgrade, representing the Serbian-led remnants of the collective Yugoslav government, said Saturday such a step would be illegal, destroy prospects for peace, and threaten security in the entire region. Even Croatia, whose hopes of a separate existence depend on early recognition, admitted the immediate effect might be to increase the scale of fighting by its forces against Serbian irregulars and the Serb-led federal Army. Serbian presidential adviser Zeljko Simic said Germany's promise of unilateral recognition by Christmas contravened "the principle that external borders are inviolable." The Yugoslav presidency, reduced by the defection of four of the country's six republics, urged international bodies to prevent the recognition of Croatia and Slovenia. It told the UN Security Council, the EC, and the Conference on Security and Cooperation in Europe that recognition would be "irreversibly conducive to the overall aggravation of the situation and of stability in the region." The announcement by Germany comes despite an informal agreement reached by the UN Security Council late Saturday on a resolution that asks states to refrain from taking any action that might contribute to tension in Yugoslavia. The resolution follows unusually direct warnings from Mr. Perez de Cuellar that "uncoordinated" recognition of the two republics would undermine peace efforts aimed at ending civil war in the Balkan federation. The resolution also authorizes about 10 UN observers, including military officers, to go to Yugoslavia as soon as possible and lay the groundwork for a 10,000-man peacekeeping operation if the fighting stops. Perez de Cuellar said that recognizing Croatia and Slovenia at this time "could have grave consequences for the Balkan region as a whole" and "would seriously undermine my own efforts" to deploy a peacekeeping force. He said he was not denying the right of Croatia and Slovenia to be independent but was concerned that "early selective recognitions" could widen the conflict. But responding to a letter from the UN chief to the EC, Genscher said denying recognition would only encourage the Serbian-dominated Yugoslav Army to continue its "policy of conquest."