Ethnic Discord : Threat of U.N. Pullout Raises a ‘Nightmare Scenario’ in Bosnia : Frustrations have led to calls for deadlines on troop use. The blue-helmeted lifeline would collapse.

Threats by Western countries to pull U.N. troops out of embattled Bosnia may be as hard to deliver on as earlier promises to protect civilians here, but the prospect has nevertheless stirred fears of devastating consequences for all of the Balkans.

As fighting in the region grinds through its third year and hopes for a negotiated solution evaporate, fatigue and frustration have prompted countries contributing troops to the U.N. command to impose deadlines for a peaceful settlement or a pullout.

France has put UNPROFOR, the U.N. Protection Force, on notice that it will cut its 6,800-troop contingent by 2,500, and Britain has threatened to withdraw all 3,300 of its soldiers if the Bosnian government and Serbian nationalist rebels have not made peace in two months.

While those and similar warnings by other NATO-member countries give the impression of a new, get-tough attitude with the Bosnian combatants, the consequences of such a pullout could be lopsided and would almost guarantee a widening of the war.

British Lt. Gen. Michael Rose, the U.N. commander for 15,000 troops in Bosnia, said in interviews he is certain all sides recognize that a pullout would lead to “a nightmare scenario.”

“If we go, who is going to feed the 2.7 million people here who are totally dependent on aid?” Rose asked. “Who is going to push the peace process? The cease-fire in Sarajevo would unravel. Even in central Bosnia, where there is already a political agreement, there is the risk that everything would come unstuck.”

Without U.N. troops to protect aid convoys trying to reach hungry civilians trapped behind the front lines, deliveries to besieged pockets and this encircled capital city would have to stop, confirmed Kris Janowski, spokesman for the U.N. High Commissioner for Refugees.

Sarajevo, which the refugee agency uses as a base for feeding 440,000 Bosnians on both sides of the encircling confrontation line, is served by a humanitarian airlift now operated and protected by U.N. forces.

“If UNPROFOR pulled out, the airport would stop functioning and there would probably be a huge escalation in the fighting,” Janowski predicted. “And UNHCR cannot run an airlift under conditions of total warfare.”

The eastern Bosnian pockets of Gorazde, Srebrenica and Zepa would also likely lose their aid lifelines, because there would be no U.N. troops or armor to muscle deliveries through the Serbian rebel cordons entrapping more than 150,000 people, mostly Muslims, in those U.N.-designated havens.

The United Nations and its aid agency have observed strict neutrality throughout their nearly two years in Bosnia, feeding nearly all of the population still left here after 200,000 deaths and the flight to other countries of as many as half of the 2 million displaced.

But because the dependent Serbian civilians live in areas adjacent to their patron state of Serbia or Croatian land conquered by fellow Serbs during an earlier phase of the regional war, the nationalist rebels have less at risk with the food pipeline if they defy the peace deadline than the Muslim-led government, whose backers would be left to starve.

Despite the inequity of aid deliveries that would result from a U.N. withdrawal, officials of the Balkans force see counter-pressures that they believe should compel the Serbian rebels to quit while they are so far ahead and get what they can through negotiation.

“Implicit in a pullout is lifting of the arms embargo,” one officer said, pointing to the mounting pressures in Washington and Western Europe to nullify a 1991 U.N. prohibition of arms deliveries to what was then Yugoslavia but has since fractured into independent republics, each of which holds widely disparate shares of the old federation’s weapon stockpile.

Serbia inherited the arsenal of tanks, heavy guns and aircraft that belonged to the massive Yugoslav People’s Army, the fourth-largest force in Europe, which has given its Serbian rebel proxies in Bosnia the military might to conquer more than 70% of this republic.

“If the U.N. is forced to leave, the chances of the Serbs getting (U.N.-imposed economic) sanctions lifted is zero and they have to worry about the Muslims being rearmed,” another European officer noted. “In both respects, time would not be on the Serbs’ side.”

Bosnia’s Muslims and Croats had been fighting each other in a war-within-a-war until March, when a U.S.-brokered agreement restored their alliance against the Serbian land grab.

But the Serbs have so far refused to commit themselves to a proposed Bosnian federation of ethnically based ministates, preferring to press on with a quest to annex their conquered Bosnian territory to a Greater Serbia.

Officials of the Bosnian government have reacted with pique to the threats of a pullout.

Prime Minister Haris Silajdzic denounced Britain’s two-month deadline as an attempt to force the leadership of a U.N.-member state to cave in to its own destruction.

The United States recently joined Russia and European Union nations in demanding that the Bosnian combatants accept an immediate cease-fire and agree to a split of the territory that would give the Serbian rebels internationally recognized authority over half of this republic.

“There does seem to be a attitude throughout the international community now that Bosnia is already dead and it just needs a proper burial,” said a Western diplomat here who regards the ethnic partitioning ordered by the major powers at their May 13 conference in Geneva as a solution that would be a short-term one at best.

Some observers believe, though, that the threats are having the desired effect of confronting the two sides with no other option but to sit down and negotiate.

Mirko Pejanovic, a Bosnian vice president who is a non-nationalist Serb, said he sees little chance of a U.N. pullout and growing signs that the leadership is ready to compromise on the issue of how long they will cease military activities to give the peace process a chance.

The foreign ministers who met in Geneva insisted that both sides agree to a four-month cease-fire and resume negotiations that deadlocked early this year.

The Serbs insist that four months is too short, because they hope to draw out the negotiations endlessly so as to strengthen their grip on all the territory they now hold. The government, fearing that delaying tactic, wants a finite term by which a fair settlement is negotiated or the intransigent party punished for refusing to bargain in good faith.

“Whether it is one, two or three months isn’t what is important,” Pejanovic contended. “There is no military solution to this conflict, so both sides must realize there is nothing to be gained by continuing to fight.”

A well-known political analyst for the Sarajevo daily Oslobodjenje, Merhet Husic, agrees the risk of a U.N. pullout is extremely slim, for the same reason cited by Pejanovic--that the two sides are likely to accept the logic of negotiations. But he also believes that the international community’s prestige is at stake.

“They’re bluffing,” he said of the British and French threats to withdraw from Bosnia. “They have to be here for the sake of their own political futures. They don’t care about Bosnia, but if they leave this place while war continues, they would be admitting they are nothing, that not even NATO can protect people from senseless killing.”

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Despite the obvious dangers of a U.N. pullout, officials warn that political realities in the parliaments of Europe could pressure those governments to put a limit on their patience and a mission whose costs and casualties have become increasingly difficult to defend.

“There will come a stage where they have to say, ‘That’s it,’ ” Rose’s aide, Lt. Col. Simon Shadbolt, said of the growing sentiment for giving the combatants an ultimatum to make peace. “We are not yet at that stage, and the mission will continue. But if we have provided the conditions for the peace process and both sides make clear they do not want peace, there will come a stage where we have to ask ourselves what the hell we’re doing here.”