EVERY noon for the past week, buses have been departing downtown Belgrade carrying volunteers to join rebel Serbian forces fighting to halt the Croatian Army offensive along the central Adriatic coast.
Dedicated Serb nationalists, the volunteers are the only overt outside military support going to the self-declared Krajina state that rebel Serbs proclaimed on the 35 percent of Croatia they conquered in the 1991 war.
For the first time since the Yugoslav crisis erupted, Serbia and its tiny dependent province, Montenegro, are demonstrating unprecedented restraint despite the advances by Croatia's troops and the rebel Serbs' constant pleas for help.
"It's definitely unusual given the pattern of the last couple of years," one Western European diplomat says.
Instead of responding to force with force as in the past, the remnants of former Yugoslavia are deferring for now to the international community to deal with Croatian President Franjo Tudjman's violation of a year-long cease-fire.
"It is necessary to immediately stop all war activities and support the peace process. This is the strategic stand of Yugoslavia," Foreign Minister Ilija Djukic said.
Political analysts cited several reasons for the shift to diplomacy, and that they pertain as much to the situation in Bosnia-Herzegovina as to the fighting in Croatia.
Most importantly, rump Yugoslavia is desperate to avert foreign intervention against Serbian forces in Bosnia-Herzegovina and a tightening of the UN economic sanctions imposed on Serbia and Montenegro for backing the Serbian territorial conquests there.
Serbian President Slobodan Milosevic, the paramount power in rump Yugoslavia, apparently believes that cooperation with international calls for a cease-fire in Croatia can stave off both threats, analysts said.
In addition, Mr. Milosevic sees cooperation as benefiting his Bosnian Serb proxies in their demand for changes in the peace plan proposed by UN envoy Cyrus Vance and Lord David Owen of the European Community. That is especially important as the Geneva negotiations have stalled over the plan, prompting Mr. Vance and Mr. Owen to defer to the UN Security Council.
"They [the Serbs] are now looking at diplomacy as a first priority, because in terms of the military situation in Bosnia, they have gotten all they want," said a Western diplomat, referring to the Serbian conquest of some 70 percent of the former Yugoslav republic.
Furthermore, Milosevic and other Serbian leaders, including the Yugoslav Army high command, recognize the Croatian offensive as an opportunity to restate their contention that they have been unfairly blamed and condemned for the violence in former Yugoslavia.
In doing so, they seek to regain some badly needed international goodwill, and possibly even support.
In particular, Russia, which is a permanent member of the UN Security Council, could use its veto power to obstruct further actions against Serbia and Montenegro.
Russian President Boris Yeltsin, under pressure at home from pro-Serbia conservatives enraged by his cooperation with the West, has already threatened to press for economic sanctions against Croatia.
"If they [Serbia] injected themselves into the fighting in Croatia, that would undermine directly the position the Russians have taken in the UN Security Council in terms of strong condemnation of Croatia and raising the possibility of sanctions," says a Western diplomat. "They are being smart, and Tudjman's move increasingly looks like a blunder," he says.
Political analysts emphasized that there is also a practical military dimension to the shift in policy, pointing to the enormous difficulties the Yugoslav Army would have intervening in Croatia.
Severe shortages of funds, raw materials, spare parts and fuel for the Army, caused by UN sanctions, have left it in no shape to fight a major conflict.
Furthermore, to reach flash points in Croatia, the Yugoslav Army would have only two options:
* A massive shipment of troops and materiel driven through Bosnia-Herzegovina along a land corridor constantly exposed to Croatian and Muslim attacks.
* Or a huge airlift that would violate the UN no-fly zone over Bosnia, something the Army may be unable to mount because of resource shortages and an action that would undermine Serbia's diplomatic initiative.
"The Yugoslav Army cannot do much because it is tied by foreign political considerations and the critical state the technical resources are in," writes Milos Vasic, military affairs analyst for the magazine Vreme.
But Milosevic, the Yugoslav Army, and other Serbian leaders could come under pressure to act against Croatia from powerful right-wing politicians as well as Serbian rebel leaders in Croatia and Bosnia-Herzegovina.
How long they could resist would depend on whether international action were strong enough to halt the Croatian offensive, which shows no sign of ending.
"It would be hard to believe that a further escalation would not be to the advantage of the Serbian nationalist hawks, and that Yugoslavia, regardless of its restraint, would not intervene," says Vreme writer Filip Svarm.