Leading Article: America's coup in Bosnia's quagmire

AT LAST there are real grounds for hope that the three-sided war in Bosnia can be brought to an end. The agreement brokered by the Americans appears to have clinched last week's ceasefire between the Croats and Muslims and laid the groundwork of a political settlement. The Bosnian Serbs, too, are showing signs of readiness to stop fighting and do a deal. They have continued to observe the ceasefire in Sarajevo and have now, under Russian pressure, agreed to stop shelling Tuzla airport.

The Bosnian Serbs fear that the Bosnian Croats and Muslims, backed by Croatian forces, may soon seek to regain some lost territory. It would therefore be surprising if the Serbs too are not ready to cease hostilities, providing they can keep most of what they have gained.

The Croat-Muslim deal envisages the creation of a federation consisting of territory controlled by the two sides within Bosnia, linked to Croatia in a looser confederation. The territorial integrity of Bosnia- Herzegovina would be maintained if the Bosnian Serbs agreed to coexist within the federation. But it seems likelier they will wish to coalesce with an enlarged Serbia: a disagreeable prospect for the pockets of Muslims that would be left behind, and - if accepted - an acknowledgement by the West that borders can be changed by force. Serbia's enlargement would also be viewed with alarm by the large minorities of ethnic Albanians and Hungarians within Serbia proper, in Kosovo and Vojvodina.

Vulnerable though it may prove, the Croat-Muslim deal is a notable coup for US diplomacy. Good timing played its part. Muslim forces were in the ascendant in the war between the two former allies. The Croats had good reason to agree to last Thursday's ceasefire, and to come to terms with a determined and increasingly well-armed opponent. The gains for the Muslims include an end to their suffering in beleagured cities such as Mostar; and more Lebensraum than envisaged in the patchwork of Indian- style reservations proposed in the Vance-Owen plan.

The Americans have been shrewd in seeing that if agreement can be reached between two sides, potential pressure on the third is increased; and they were probably wise to put principles before maps. The Europeans worked the other way around, and seemed too anxious - certainly to American and German eyes - to propitiate the main aggressors, the Serbs.

From their painful experience in brokering the Middle East peace talks, the Americans have learnt that to achieve results, constant bullying and cajoling are needed. If there is to be a lasting peace in Bosnia, the same judicious application of carrot and stick will be needed over years rather than months.

At the same time, the Russians must lean on the Bosnian Serbs and their patrons in Belgrade. Against the long-term danger of the Serbs being manipulated by an ultra-nationalist regime in Moscow should be set the undesirability for President Yeltsin of being associated with Serb aggression. For Russia, too, involvement in former Yugoslavia is not without its potential quagmires.