Leading Article: Some hope amid the hazards

HOPE, scepticism and anxiety are among the responses evoked by Nato's threatened air strikes against Serbian artillery positions around Sarajevo, and the ceasefire now in force in that tragic city. Scepticism is liable to predominate. There have been many ceasefires between the Serbs and Muslims in the Bosnian capital. All have been broken, with the Serbs soon resuming their pitiless bombardment. Equally, Nato has threatened air strikes to break the siege of Sarajevo before - last August and last month.

No action ensued because no order came from the UN's secretary general, Boutros Boutros-Ghali. His authorisation would still be required for strikes before the expiry of the 10-day deadline for the withdrawal of heavy Serbian weapons beyond the 20km exclusion zone. But after that, attacks could take place merely 'in close co-operation' with Mr Boutros-Ghali.

The climate of opinion in the West seems to have been genuinely changed by last Saturday's slaughter, in which 68 people were killed and almost 200 wounded by a single shell thought to be of Serb origin. For the first time since it was founded in 1949 as a defensive organisation, Nato is poised to take offensive action. The Bosnian Serbs do not appreciate the extent of this change. Yesterday they were refusing to bow to the ultimatum, and Radovan Karadzic walked out of the Geneva peace talks.

The dangers ahead are numerous. Even if, say, pressure from Belgrade brings about a change of heart, the Serbs will try to spin out their withdrawal and maintain pressure on Sarajevo and on UN troops by one means or another. They could, for example, use UN troops monitoring the withdrawal as human shields while resuming their bombardment. The Muslims for their part may seek to provoke the Bosnian Serbs into action, perhaps by simulating a Serb attack. In this civil war, none of the combatants can be trusted.

Several important questions remain unanswered. One is whether Nato has any concept of how air strikes could contribute to a negotiated settlement of the three-sided conflict. Another is whether, should grave complications arise, there is readiness to send in extra troops - perhaps to save those already there. A third question concerns Russian reactions.

Arguably, western interests are more affected by the well-being of Poland, Hungary, the Czech Republic and the Baltic states than by a Balkan civil war. Yet if Nato attacks on fellow Slavs in Bosnia inflame Russian nationalism, the Russians could prove very obstructive to the progressive absorption of those countries into Nato and the European Union. Yet for all these fears, there must be relief that the West at last seems to mean what it says - and may even act on it.