THE Bosnian Serb siege on the eastern Muslim town of Srebrenica has become the most crucial challenge encountered by the international operations in war-ravaged Bosnia-Herzegovina.
Most important is saving the lives of the estimated 40,000 residents and refugees trapped for months with little food and shelter in the shell-ruined town.
But as Bosnian Serb forces close in around Srebrenica, United Nations officials concede that the credibility of their entire effort in Bosnia also rides on preventing Bosnian Serb forces from capturing the town and completing their "ethnic cleansing" of the republic's northeastern flank bordering Serbia.
"For the UN presence in Bosnia-Herzegovina, Srebrenica is an important test," says a senior UN official, speaking on condition of anonymity. "If Srebrenica falls ... something has to be reassessed in the whole operation, because this is violently in contravention of any humanitarian principle."
Despite Bosnian Serb guarantees of a cease-fire, UN officials reported that shells struck near relief operations outside Srebrenica over the weekend.
The town's capture is widely regarded as a military and political necessity for the Bosnian Serb leadership. Its fall would give the Bosnian Serbs unopposed control of the northeastern Drina River border with Serbia - their economic, political, and military benefactor.
A Serb victory in Srebrenica also could spell an end to the current international peace plan for Bosnia, which the Bosnian Serbs have refused to accept. (UN Security Council to tighten sanctions, Page 9.)
Under the plan, which would divide Bosnia into 10 ethnic-based provinces, the Srebrenica area would fall within one of three proposed Muslim-dominated regions. That would block territorial continuity between the proposed Serb-dominated provinces and Serbia, obstructing the Bosnian Serbs' ultimate aim of joining their areas to the neighboring republic.
Relations between the UN and the Bosnian Serbs are increasingly strained. Ammunition was found in a UN aid truck last week, outraging the Serbs, and NATO begins enforcing the no-fly zone over Bosnia today.
"It's clear to us that UNPROFOR [the UN Protection Forces in Bosnia] has been aiding our enemy from the start," Bosnian Serb leader Radovan Karadzic said to the Yugoslav news agency, Tanjug.
The world spotlight fell on Srebrenica when French Lt. Gen. Philippe Morillon, the UNPROFOR commander for Bosnia, spent several days there last month as Serb forces advanced.
General Morillon placed the UN's prestige on the line by vowing to save Srebrenica. It was the most ambitious pledge any UN commander has made on behalf of a mission that is restricted to protecting relief operations. Withdrawing refugees
Strengthened by a new UN Security Council resolution to aid Srebrenica, Morillon and UN relief officials have begun evacuating the refugees who have flooded the town over the past year as they fled Bosnian Serb attacks on surrounding areas.
About 7,600 have been evacuated in four UN convoys to Tuzla, the only city left in northern Bosnia still controlled by forces loyal to the Muslim-led government.
Jose-Maria Mendiluce, special envoy to Yugoslavia of the UN High Commissioner for Refugees (UNHCR), said the evacuations are intended to help Srebrenica's 10,000 original residents remain there by making it easier for his agency and other organizations to feed and care for them.
The evacuations were initially opposed by the Bosnian government and the authorities in Tuzla and Srebrenica, who viewed them as aiding Bosnian Serb "ethnic cleansing," a charge Mendiluce rejected last week.
"Even if it helps `ethnic cleansing' by the Serbs, every 2,000 people we bring here is a testimony to what the Serbs are doing to the Muslims," he said.
Another UN goal is the permanent deployment of UNPROFOR troops in Srebrenica, a demand made by Bosnian officials in return for allowing the evacuations.
That will be much harder to achieve. Morillon last week attempted without the permission of Bosnian Serb leaders to lead a contingent of about 170 Canadian troops into Srebrenica. But about 300 Bosnian Serb protesters - believed to have been mobilized by local Bosnian Serb authorities - blocked the road.
The crowds mobbed Morillon's armored personnel carrier, tore off the aerial, and painted insulting graffiti and Serbian nationalist symbols all over the vehicle. Commander rejects UN
Gen. Ratko Mladic, the Serb military commander, refused to permit UN troops into Srebrenica after meeting with UNPROFOR commander for Yugoslavia, Swedish Gen. Lars-Erik Wahlgren, in Belgrade Friday.
But he agreed to extend to Srebrenica Bosnia's two-week-old cease-fire. That move, UN officials say, was predictable because the permanent presence of UN troops would make it much harder for Bosnian Serb forces to overrun Srebrenica.
"UNPROFOR's objective is to be present and to be there to reassure the population and to make more difficult a military offensive against the civilian population," Mr. Mendiluce said. But he conceded that 150 men "is not a deterent force" capable of defending the town.
"But you are forcing those who may decide to continue the offensive to put at risk 150 soldiers who are UNPROFOR soldiers, as well as UNHCR staff," Mendiluce said. "It will certainly be more costly."