Refugees Flee Fighting in Bihac : Bosnia: Serb rebels threaten to overrun a third ‘safe area.’ U.N. officials fear humanitarian disaster as 8,000 people rush to escape enclave.

Fierce Serb attacks drove thousands of refugees into flight in the northwestern Muslim enclave of Bihac on Wednesday and triggered a Bosnian government warning that the area could become the next U.N.-designated “safe area” to fall.

At least 8,000 refugees fled ahead of advancing Serbs in the Bosnian enclave bordering Croatia in what U.N. officials called “a humanitarian disaster in the making.”

Chris Gunness, a U.N. spokesman in Zagreb, said attacks by Croatian and Bosnian Serb units had driven across almost a third of the enclave--about 40 square miles--where 180,000 Muslims have been trapped. In a region hard-pressed for food, the captured area included almost a quarter of all farmland at harvest time.

U.N. officials said the refugees appeared to be heading for the central town of Cazin, while Serb artillery and infantry staked out new claims for territory behind them.

The town of Bihac, the enclave capital, is among the four remaining Muslim safe areas proclaimed by the United Nations two years ago. The others are Sarajevo, Tuzla and Gorazde. A fifth, Srebrenica, fell two weeks ago; the sixth, Zepa, fell Tuesday to Bosnian Serbs, and its refugees began to spill into Bosnian government-controlled areas Wednesday.

In Sarajevo, Bosnian Prime Minister Haris Silajdzic told reporters that Bihac is in jeopardy. “As terrible as things are in Zepa today, the situation in Bihac is even more significant,” he said. “The Serbs have an unprecedented number of troops around Bihac. The safe area is at obvious risk. The world must do something now, make good on its promises.”

U.N. officials said the Serb attacks were coordinated: Bosnian Serbs from the east, Croatian Serbs from the west. From the north, a rebel Muslim group was also attacking hard-pressed Bosnian government forces.

“I hope we will endure now, but it is quite difficult,” Gen. Atif Dudakovic, commander of the Bosnian government 5th Corps, told Croatian Television from Bihac.

In Brussels, NATO Secretary General Willy Claes warned that air strikes, which would be ordered in response to any Serb attack on Gorazde, could be extended to Bihac.

The Croatian government agreed last weekend to help defend the enclave, and U.N. observers have reported major troop, artillery and tank movements near the enclave, Gunness said. In Washington, the State Department said units of the Croatian army were in action near Bihac and added it had advised the Croatian government against pressing the conflict.

“What we are seeing in Bihac is exactly what went on in Srebrenica,” the angry Bosnian prime minister said at a Sarajevo news conference. “We warned them then, and the response we got was that Srebrenica was not under threat. Srebrenica was a colossal betrayal by the U.N. . . . The question arises: Are we now witnessing the same betrayal of Bihac?”

Fikret Abdic--a businessman wanted for fraud in Austria and the rebel Muslim supporting the Serb assault--Wednesday proclaimed a “Republic of Western Bosnia” in northern Bihac, an area he had previously declared to be autonomous. Diplomats called the action meaningless.

Military observers here worry, however, that fresh gains by the Serbs and Abdic forces could provoke major Croatian intervention. The fall of Bihac would dash Croat hopes of reconquering Serb-held lands in Croatia west of the enclave.

Silajdzic said he was eager for direct Croatian military aid: “We do need help from Croatia. We do hope the Croatian army and the HVO [Bosnian Croat militia] will do whatever they can. This is the moment of truth.”