The rapid ascendancy of Kosovo's ethnic Albanian guerrillas, who now control about a third of the territory in the restive Serbian province, has greatly complicated the political and military challenges confronting the West as it tries to contain the conflict.

While NATO planners refine options for military action ranging from airstrikes to ground troops, officials from the United States, Russia and four European powers comprising the Balkans "contact group" will meet in Bonn Wednesday to consider drafting their own blueprint to restore political autonomy to the ethnic Albanians, who make up 90 percent of the population in Kosovo.

"I think we should draw up an outline within the contact group for autonomy because it is apparent that neither side is in a position to do this," German Foreign Minister Klaus Kinkel said on German television. "We then have to consider how we can guarantee autonomy, for both sides."

But senior U.S. and European officials say the swiftly changing nature of the conflict illustrates the enormous difficulties of restoring peace in the province, where more than 300 people have been killed in a four-month Serbian offensive against the separatist guerrillas.

While focusing pressure on President Slobodan Milosevic of Yugoslavia to restrain his security forces, the contact group is also scrambling to find ways to curb the ambitions of the Kosovo Liberation Army (KLA), which has been described as the world's fastest-growing guerrilla army. Serbia is Yugoslavia's dominant republic.

The rebel group, which receives funds from Albanian exiles abroad and arms from neighboring Albania, has developed into a hydra-headed guerrilla force with five regional commands that loosely coordinate operations but do not submit to any higher political authority, according to diplomats.

The United States has been trying to persuade representatives of the guerrillas to join Kosovo's elected ethnic Albanian leader, Ibrahim Rugova, in sitting down for peace talks with Milosevic and the Serbian leadership. But their commanders are said to loathe the pacifist Rugova and believe his support is rapidly diminishing among Kosovo's 1.8 million ethnic Albanians.

"The problem in dealing with the Kosovo Albanians is that Rugova may have legitimacy as an elected leader but he has very little power, while the KLA, which is gaining power rapidly, does not have the legitimacy," a senior European diplomat said.

The guerrillas' armed independence campaign has been emboldened by its military successes. Jakup Krasniqi, who was identified by NATO officials as a prominent rebel spokesman, told the German newsweekly Der Spiegel that the guerrillas' goal is to establish a greater Albania that would unite all ethnic Albanians living in the Balkans in a single country. That would suggest that the KLA would like to incorporate Kosovo, Albania proper, and territory occupied by 400,000 ethnic Albanians estimated to be living in Macedonia.

U.S. and European officials say any ambition by the guerrillas to establish a greater Albania would pose the greatest danger of sparking a wider Balkan war since Milosevic's forces launched their crackdown in late February.

American envoy Richard C. Holbrooke, the newly nominated U.S. ambassador to the United Nations, failed in his recent diplomatic mission to Serbia to identify credible representatives of the guerrillas, let alone persuade the insurgents to cease hostilities, tone down demands and work toward a political compromise.

U.S. and European officials say contact group efforts to conceive something between autonomy and independence -- by proposing, for example, to make Kosovo the third republic within Yugoslavia along with Serbia and Montenegro -- have foundered because of stiff Russian resistance. They say the Russians, feeling bruised by their own war with separatists in the region of Chechyna, insist that autonomy for Kosovo must be kept within the realm of Serbia.

Milosevic stripped Kosovo of its autonomy in 1989 and imposed direct Serbian rule.

The attempt to draw up a settlement proposal could foreshadow the kind of intensive negotiations that Holbrooke orchestrated at Dayton, Ohio, in brokering a deal that ended the Bosnian war in 1995. "We are moving toward the stage where the only possible solution may be to lock up both sides and throw away the key until they agree to a deal," the senior European diplomat said.

That prospect has already been accounted for in the military planning at NATO headquarters, where the Western military alliance is bracing for another peacekeeping mission that could be even more tricky than its tasks in Bosnia.

After first exploring ways to contain the Kosovo conflict by shielding Albania and Macedonia, then brandishing the threat of airstrikes against Yugoslavia to compel the Serbs to ease their crackdown, NATO is now scrutinizing the possibility of air and ground operations that would enforce a negotiated peace in Kosovo along the lines of their mission in Bosnia, according to NATO officials.

"It's a very fluid situation and the priorities seem to change by the minute, but we need to keep a whole spectrum of military options in play," a senior NATO official said. "We could be called upon to use force in many circumstances, and that includes imposing a settlement without the consent of the parties."