THE various European Community-brokered cease-fires and agreements in Yugoslavia - between the federal government and the breakaway republics of Slovenia and Croatia - belie one fact: These republics are dead set on leaving the Yugoslav federation. Whatever agreements they make are aimed at that goal.Slovenia, for example, may have agreed to defer its total independence - saying it would turn over customs profits at its border posts in exchange for controlling those posts. But these are conditions it was willing to accept all along. More telling, Slovenia's delegate to the federal presidency, Janesz Drnovsek, has still not shown up for meetings in Belgrade. Nor will he. Slovenia will do just enough to keep a fragile peace alive while trying to exit Yugoslavia. The real problem at this juncture, however, is not Slovenia but Croatia. Croatia is slipping toward a major conflict with the Serbian-led Yugoslav Army. It isn't yet clear what will or can stop this conflict from occurring. Croatia's departure would seal the end of Yugoslavia. Croatia was slower to assert the independence it jointly declared with Slovenia on June 26, and its terms and conditions were more vague. But that's because its position, with 11 percent of its population Serbian, is more explosive. The federal Army occupies large segments of Croatia. It's largest barracks, the Marshall Tito barracks, are in Zagreb, Croatia's capital. Serbian leader Slobodan Milosevich says he is committed to fight on behalf of the Serbs in Croatia. The independence movement in the Balkans has brought with it a whole new wave of settling old scores. Again, these scores are between Serbs and Croats. They have to do with the enormous cultural chasms between the two groups, as well as atrocities committed by Nazi Croats against the Serbian population during World War II. The slippage toward conflict in Croatia may seem inexorable, but it must be stopped - or at least defused. This may require solutions as radical as ceding some territory to Serbia. Currently, Yugoslavia is breaking apart by itself. The Croats should bide their time a bit longer.