Aid Officials in Bosnia Fear They’ve Done All They Can : Balkans: Attacks consistently frustrate efforts to bring in food, medical supplies. Western countries may decide risks outweigh the benefits.

After Serbian tank fire killed four aid workers and three relief planes were fired on while bringing food into besieged Sarajevo, Western aid officials said Thursday that they fear they have reached the limit of what they can do to help civilians trapped in a raging war zone.

Humanitarian relief flights that provide 90% of Sarajevo’s food have been suspended for the last two days because of attacks on U.S. and other Western aircraft taking part in the lifesaving mission. An official of the Office of the U.N. High Commissioner for Refugees expressed uncertainty over when, or if, the deliveries will resume.

Truck convoys that carry the bulk of food and medical aid to other areas of Bosnia have also failed in recent days to deliver their cargo to those who need it because of fierce fighting along the roads and deliberate attacks on those risking their lives to bring it in.

“It is an absolutely horrific situation,” said the U.N. refugee agency’s Sarajevo representative, Tony Land, after describing an incident earlier this week near the embattled northern town of Maglaj in which the four aid workers were killed.

He detailed numerous attacks and incidents in which humanitarian convoys have been blocked or had their goods hijacked, and he concluded that the foreign countries taking part in the mission are reaching a point where they have to weigh the sporadic benefits against the tremendous risks their pilots and drivers are taking.

“Every landing and every takeoff is made under battle conditions,” Land said of the Sarajevo airlift.

A bullet struck a U.S. military plane in the fuselage during a delivery here Tuesday, and a German aircraft reported that antiaircraft radar had locked onto it during its flight between here and the relief base in Split, Croatia. The German incident was the third report in as many days of a missile lock-on, a U.N. military source said.

The attacks prompted the U.N. refugee agency to suspend aid flights indefinitely, but Land indicated that his organization remains committed to easing the plight of Bosnian civilians as much as it still can.

“Our job is simply to feed hungry, suffering people,” he said. “The key thing is that there are a lot more hungry, suffering people than there are men with guns.”

But participating countries are becoming doubtful of the mission in which dozens of their troops and aid workers have been killed and hundreds injured.

The nine-truck U.N. convoy attacked in Maglaj had holed up in a tunnel just outside of the town to shelter themselves from shelling and sniper fire while waiting to unload at a warehouse just a few hundred yards ahead.

Land said artillery and small-arms fire on idled convoys has become so routine that drivers now seek cover while waiting.

But in this case, while 12 Danish aid workers and four Bosnian assistants huddled in the half-mile-long road tunnel Tuesday, shells were fired into the entrance, killing four and seriously wounding two others.

“Three things are very clear,” reported Maj. Luuk Niessen, spokesman for the 9,000-strong U.N. Protection Force in Bosnia. “This has been a deliberate attack on a UNHCR convoy, the attack came from the direction of Serb-held positions and tank rounds were used.”

Two heavily armored Warrior vehicles and their British crews were escorting the convoy, but they did not return fire, Land said.

U.N. troops in Bosnia currently have no peacekeeping mandate. Their mission is solely to escort aid convoys, and they are authorized to use force only in self-defense and when the source of the attack is identifiable. It was not clear why the British soldiers refrained from firing back, since it was probably their account of the attack that led U.N. commanders here to conclude that it came from Serbian positions.

U.N. military and humanitarian sources have expressed reluctance to use force in some situations where it might be permissible for fear of antagonizing the heavily armed Serbs, who could retaliate against U.N. troops deployed in vulnerable areas or stop allowing even the occasional food convoy to reach Bosnian Muslims or Croats.

Serbs have lately resumed the offensive after a retreat by Washington and its European allies from threats to use force to halt the Serbian tide sweeping across Bosnia.

The United States, Russia and Western Europe have lately abandoned a U.N.-backed peace plan that the Serbs object to in favor of a proposal that would herd Bosnians into six U.N.-protected sanctuaries--Sarajevo, Tuzla, Gorazde, Bihac, Srebrenica and Zepa.

Washington’s call for military air strikes and a lifting of the blanket arms embargo for the embattled Bosnian government forces was rejected by reluctant European allies, prompting the international community to draw up the “safe havens” plan instead.

The six proposed protected zones have sustained such violence in recent weeks that one U.N. official drew a sign at a news conference that warned: “Safe Area: Extremely Dangerous--Keep Out.”