Bosnians Rebuff Last-Minute U.N. Peace Effort : Balkans: Muslim government and rebel Serbs reject continuing cease-fire that ends today.

As a cease-fire that has existed in name only loses even that meager status, the enemies in Bosnia-Herzegovina’s relentless war are giving every indication they plan to continue killing each other.

Both the Muslim-led Bosnian government and Bosnian Serb rebels rebuffed last-minute efforts by U.N. peacekeeping officials Sunday to extend the four-month cease-fire.

The truce, which expires today at noon Bosnia time, was brokered by former President Jimmy Carter but brought only fleeting relief to this embattled region.

Already, fighting has intensified steadily across northern and central Bosnia and in the besieged capital of Sarajevo, where Bosnian Serb rebels have virtually shut down the airport, one of the city’s last links with the world.

Signs that the war could widen pop up daily. Although not parties to the fading cease-fire, Croats and Croatian Serbs clashed over the weekend in violence that ended with the Serbs blocking a strategic Croatian highway that only recently had been reopened in a gesture of “confidence-building” cooperation.

And Serbs flying warplanes from Croatia were suspected of dropping two cluster bombs on Bosnian army positions near the northwestern Bosnian enclave of Bihac on Saturday, according to U.N. officials who were investigating the incident Sunday. Such an attack would be a violation of the U.N.-declared “no-fly” zone, similar to incidents in November that triggered a retaliatory assault by the North Atlantic Treaty Organization on a Serb-held air base.

In fact, the Bosnia cease-fire essentially collapsed weeks ago and has served mostly as a period of regrouping and rearming for the government army and its Serbian foes, analysts and diplomats say.

On Sunday, Yasushi Akashi, the U.N. special envoy for the Balkans, met with Bosnian government officials in Sarajevo and with Bosnian Serb leaders at their headquarters in Pale, imploring both sides to at least temporarily extend the formal cease-fire. But neither faction would budge, U.N. officials said.

Bosnian Prime Minister Haris Silajdzic told reporters that accepting an extension would be tantamount to participating “in the legalization of the occupation of our country.”

“This is something we shall not do,” he said.

Silajdzic offered to show “restraint,” however, if the Serbs do not harass food convoys or shell civilian areas--both of which they do routinely.

Later Sunday in Pale, 10 miles east of Sarajevo, Bosnian Serb leader Radovan Karadzic reiterated his position linking any new cease-fire to the lifting of sanctions.

Akashi’s failure to gain even the slightest agreement comes as France and other countries involved in the United Nations’ hapless peacekeeping mission are hinting that they will withdraw if the cease-fire is not extended.

The United Nations has seen its peacekeepers killed, attacked and humiliated when hostilities have supposedly been on hold. Two French peacekeepers were killed by snipers in a single week last month.

A withdrawal by the United Nations would undoubtedly unleash an even more brutal and widespread level of warfare, diplomats say. Some say, however, that they believe the dire consequences of any withdrawal would ultimately prevent major governments from acting on such pullout threats.

Diplomats and other analysts say it is the Bosnian army that has benefited the most during the cease-fire, using it to build up its troop strength, to train and to continue incorporating small arms and light artillery.

In March and April, government troops launched coordinated attacks on Serbian positions, capturing Mt. Vlasic in northern Bosnia, the site of a strategic Serbian communications tower, and pounding the Majevica hills in central Bosnia in an ongoing attempt to cut off Serbian supply routes near the town of Brcko.

Better organized now,than before, but still outgunned by the Serbs, the Bosnian troops apparently have been trying to keep the Serbs overextended and vulnerable to attack.

The Serbs have yet to respond with a coordinated counteroffensive. Although suffering from the toll that sanctions and political isolation are taking, the Serbs continue to control nearly 70% of Bosnia’s territory, a status quo essentially frozen during the cease-fire.

Rather than full-scale war, several analysts predict a continuation of escalating, sporadic government offensives and escalating Serbian retaliations.

“It will take years for there to be a dramatic shifting of tables,” said one diplomat who watches the Balkans. “You’ll see a static confrontation, at least in the short term, with a little movement here, a little movement there. Both sides will make small gains, but at enormous loss.”