MAASTRICHT, NETHERLANDS — ANXIOUS not to have their summit on monetary union derailed, European Community leaders have sought to buy themselves time here by putting off any substantial discussion of events in the former Soviet Union and Yugoslavia.A Dec. 16 meeting of EC foreign ministers, already scheduled to take up the divisive Yugoslav issue, will now also consider the Soviet Union's disintegration and the Dec. 8 declaration of a new commonwealth by Russia, the Ukraine, and Byelorussia. But EC leaders were unable to ignore the threat that destabilization of the former Soviet Union presents for Europe and dispatched a Dutch emissary to the former Soviet Union's three Slavic republics. One EC official said the message would "hammer at the point that as holders of nuclear arms on their soil, the three republics have a life-threatening responsibility to respect international accords and to act seriously." Danish Foreign Minister Uffe Ellemann-Jensen told journalists that the Soviet Union could become "like Yugoslavia," with the chilling nuclear dimension added. An EC declaration on the Soviet Union is expected at the end of the summit. France proposed criteria for recognition of newly declared countries, including respect of democratic principles, rule of law, and human and minority rights. The idea follows German Chancellor Helmut Kohl's promise to recognize Croatia and Slovenia by Christmas.