NEWS ANALYSIS : Future Risky for Yugoslav Mission : Diplomacy: All sides want U.N. peacekeeping troops sent in, but each has its own idea about how they should be used.

Former U.S. Secretary of State Cyrus R. Vance, the United Nations’ special envoy for Yugoslavia, arrives in this war-torn country Saturday to work out a strategy for the organization’s first armed intervention in Europe, a dangerous $200-million mission fraught at every step with potential failure.

Although Serbia, Croatia and the Yugoslav federal army all have called for U.N. peacekeeping troops to end their civil war, each has its own terms for where the force will be allowed to deploy.

A primary condition for U.N. intervention is a stable cease-fire throughout the region, which has proved elusive despite 14 internationally mediated attempts.

The latest truce brokered by Vance and European Community diplomats last weekend has deterred fighting in many areas of Croatia but fallen far short of halting the bloodshed. Fighting around the central Croatian town of Lipik, about 70 miles southeast of Zagreb, left about 30 dead Thursday, according to the news agency Tanjug. Croatian radio said the federal army attacked villages in the ethnically mixed area with artillery, mortars and infantry.

For the first time in days, there were no reports of fighting or shelling around the east Croatian city of Osijek, where Serbian and federal army assaults reportedly killed 19 people Wednesday.

Vance brings with him a message from U.N. Secretary General Javier Perez de Cuellar that unless the cease-fire is strictly observed, there will be no U.N. intervention. The threat to abandon the Yugoslav crisis strikes fear in many civilians, who have tired of the deadly conflict and the disruptions it has imposed on their lives. But thwarting the U.N. efforts may be what some combatants want.

The Serbian-led Yugoslav Peoples Army, well armed and fully mobilized, has already conquered one-third of Croatia and turned the territory over to militantly nationalist Serbs. It appears to have set its sights on the area around Osijek as the next swath of Croatia to be seized, encircling the predominantly Croatian city of 140,000 with tanks and heavy artillery.

The Serbian government has already proclaimed eastern Croatia a new autonomous Serbian province and begun resettling Serbian refugees from other areas of Croatia in the homes from which families of other nationalities have fled.

At the village of Erdut, temporary regional capital of the purported province, a Serbian guerrilla leader made clear this week that his irregular forces would never be replaced by U.N. troops.

“United Nations forces are welcome in Croatia, but they should be sent to Zagreb. They aren’t needed here,” insisted Zeljko Raznjatovic, a reputed Belgrade underworld figure better known by his military code-name, Arkan.

Like most of the Serbian fighters, Arkan and his Serbian Tigers guerrilla force do not consider the occupied regions to be part of Croatia; therefore, they believe them to be exempt from a U.N. condition that all areas of conflict in Croatia be demilitarized.

Federal Defense Minister Veljko Kadijevic has so far gone along with Belgrade’s appeals for U.N. intervention, but if the army is ordered out of the trouble spots in Croatia and Bosnia-Herzegovina, the hard-line military leadership is widely expected to balk.

Withdrawal from Croatia and Bosnia-Herzegovina would cut the federal army’s mandate down to defense of Serbia and the impoverished republics of Macedonia and Montenegro, as the westernmost republic of Slovenia has already been cleared of Yugoslav troops. The three remaining republics could not support the top-heavy federal army, which consumed as much as two-thirds of the Yugoslav budget in better days.

Aside from the risks of army brass and Serbian irregulars ignoring the U.N.’s withdrawal order, demilitarization of the Croatian crisis areas may prove unworkable for other reasons.

Croatia’s national guard and even local Croatian police units make up much of the republic’s fighting force against rebel Serbs and the army. As most guardsmen and police officers live in the communities they are charged with protecting, they would have no place to withdraw to. And in societies where virtually every adult male owns and carries a gun, disarming of the civilians and reservists on both sides would be dangerous, if not impossible.

Croatian government leaders in the capital of Zagreb want the U.N. forces to be stationed along the republic’s eastern border after federal and Serbian fighters have been cleared out. That would serve to recover for Croatia all the territory that it has lost to the Serbs in five months of war. It is a condition that neither the army nor the Serbian leadership in Belgrade would accept.

Serbian President Slobodan Milosevic has called for establishing a U.N. buffer zone along the current front line, which would set the seal on the Serbs’ territorial gains and prevent the Croats from trying to recover their land.

The army appears to be sharply divided over the need for U.N. troops in the first place and over a plan for their deployment in the unlikely event that a stable peace is ever achieved long enough for U.N. forces to move in. Defense Minister Kadijevic appears willing to settle for control of the Croatian territories already in Serbian hands, but army hard-liners such as the chief of staff, Gen. Blagoje Adzic, have made clear that they want Osijek and much of the Croatian coastline to stay under “federal” control.

Vance is reported to favor what has been termed an “inkblot” strategy for deploying the peacekeepers, which Perez de Cuellar expects to number about 10,000. Under such a plan, the troops would be clustered in ethnic trouble spots within Croatia but not linked in an impenetrable line.

The U.N. envoy’s approach would be effective only if the Security Council resolution calling for demilitarization of the conflict zones is fulfilled. Otherwise, the continuing presence of armed units could expose the peacekeepers to sniper fire by extremists.

Complicating any chance for a compromise is the involvement of unruly radicals on both the Serbian and Croatian sides. Guerrilla leaders such as Serbia’s Arkan and the ultra-nationalist Croatian Party of Rights leader Dobroslav Paraga are not party to the peace talks and heed only those orders that conform to their own military plans.

Further undermining the international peace effort is Serbia’s creeping takeover of federal government functions, which risks diplomatic isolation and withdrawal of U.N. intervention and aid.

Serbia, the largest of Yugoslavia’s six republics, already controls the federal army, the collective presidency and what is left of the Yugoslav Parliament, which is being boycotted by four of the republics.

Only federal Prime Minister Ante Markovic and his foreign minister, Budimir Loncar, remain in the Yugoslav Cabinet that last year won Western support for its efforts to transform the Communist federation of 24 million into a free-market democracy.

But Markovic and Loncar, both Croats, have been pilloried by the Serbian leadership and blamed for everything that is wrong with Yugoslavia, including the civil war. State-controlled media have branded them traitors and accused the powerless government of selling out to the West.

One house of the Serbian-dominated federal Parliament has already voted no confidence in Markovic and Loncar and appealed to the federal presidency to replace them. That action would add what is left of the Yugoslav government to the Serbian power clique.

A final vote to oust Markovic and Loncar had been set for Wednesday, but it was postponed to Dec. 5 for what the Tanjug news agency described as concern that the move could have “unfavorable international consequences.”