NEWS ANALYSIS : Christopher, Contact Group Face Hard Choices in Bosnian Conflict : Balkans: The mediators differ in their approach following Serbs’ rejection of last-chance peace deal.

Bosnian Serb rejection of a last-chance peace plan and attacks on U.N. soldiers have cornered world powers into choosing between military punishments they have no stomach for or less-daunting actions that risk worsening the Balkan bloodshed.

Rather than demonstrating international resolve to end the war in Bosnia-Herzegovina, today’s diplomatic grappling among U.S. Secretary of State Warren Christopher and four European foreign ministers is expected to bolster Serbian nationalists’ confidence that no outside power will intervene to stop their land grab.

Christopher and his counterparts from the five-nation Contact Group, as the latest assemblage of mediators in the Balkan conflict is known, are gathering here to ponder a response to the Serbs’ spurning of a proposal aimed at forcing peace in Bosnia by ethnically segregating its diverse peoples.

Serbian gunmen loyal to warlord Radovan Karadzic have underscored their opposition to the partition terms by reimposing a total blockade of Sarajevo, firing on civilians in the U.N. “safe haven” of Gorazde and attacking U.N. soldiers and aircraft attempting to deliver humanitarian aid.

Christopher and the foreign ministers of Russia, Britain, France and Germany warned earlier this month of serious consequences for any Bosnian faction refusing to endorse their formula for a settlement.

The Sarajevo government representing Muslims, Croats and others committed to an integrated Bosnia reluctantly conceded to the Contact Group’s proposal to roughly split their republic with rebel Serbs.

Karadzic’s nationalist gunmen, who have conquered and “ethnically cleansed” more than 70% of Bosnia, rejected the plan earlier this month because they want more territory and the right to add their war spoils to an emerging Greater Serbia.

In testimony before Congress on Thursday, prior to his departure for this Swiss lakeside city, Christopher said the Serbs’ intransigence means the Contact Group nations might be compelled to lift an arms embargo that has left the Bosnian government army unable to acquire weapons for defense against the heavily armed Serbs.

But French Defense Minister Francois Leotard warned the Senate Armed Services Committee that such action would trigger an immediate widening of the 27-month-old war that has already killed 250,000.

Leotard said France would not rule out providing arms to the Muslim-led government as a last resort, but he made clear his nation’s preference for a phased response to Serbian defiance.

“If you lift this arms embargo, we are on the side of the Muslim Bosnians and against the other parts (of the conflict),” Leotard told reporters in Washington.

Echoing British concerns for international peacekeepers already deployed in Bosnia, Leotard said taking sides against the Serbs would expose the U.N. Protection Force to unacceptable risks.

The nearly 40,000-strong peacekeeping force maintains a neutral stance in the conflict. Its only task is to escort aid convoys and monitor cease-fire agreements worked out by the warring sides.

Concern for British and French soldiers in Bosnia has also made those two main troop-contributing nations reluctant to endorse NATO air strikes to force Bosnian Serbs to abide by U.N. Security Council resolutions aimed at protecting civilians.

Reluctance to use military force against the Serbs has been palpable since two token North Atlantic Treaty Organization air strikes against rebel artillery in April spurred a wave of hostage-taking and harassment of the U.N. force.

British Foreign Secretary Douglas Hurd earlier this week made clear his reservations about further use of air power when he pushed for a tightening of economic sanctions against the rebels and their patrons in neighboring Serbia instead of NATO bombing sorties that might again put peacekeepers in peril.

Russia is also opposed to any use of force against the Serbs, fearing repercussions at home among nationalist politicians who accuse President Boris N. Yeltsin of kowtowing to the West rather than coming to the aid of Serbs, with whom Russians share the Orthodox religion and a Slavic heritage.

With virtually no support among the allies for military intervention to eradicate the nationalist virus, and amid obvious internal squabbles about lifting the arms embargo or conducting further air strikes, Christopher and his European colleagues appear to be leaning toward more symbolic measures.

Economic sanctions levied against the rebels’ patrons in the rump Yugoslavia more than two years ago have not dented the Serbian drive to forcibly annex huge swaths of Bosnia and Croatia.

Yet officials of the Contact Group who met here Friday to prepare for the foreign ministers’ meeting said they were focusing on measures that would first tighten the ineffectual existing sanctions, then raise the prospect of further use of NATO air power later if the rebels persist with attacks on Bosnian civilians and U.N. personnel.

With no credible threat of punishment for a series of deadly actions by the Bosnian Serbs over the past few weeks, the rebels are expected to again wait out the international attention now fleetingly focused on the intractable crisis then press on with their campaign to build an expanded Serbian state.