Leading Article: A good day for Nato and Europe

THE Nato summit that ends today in Brussels has already yielded two outstanding results. The first - uncertain though its fulfilment may be - is the deal under which Ukraine's leadership has agreed to destroy the country's nuclear arsenal in exchange for dollars 12bn. The second is the much more positive than expected tone adopted by Nato leaders towards extending membership to former members of the Soviet bloc, notably Poland, Hungary and the Czech Republic.

The Ukrainian deal will be formally signed when Bill Clinton visits Moscow later this week. It involves some 1,200 nuclear warheads left on Ukrainian soil after the collapse of the Soviet Union. The American commitment to underwrite the destruction of this potential threat to world peace is welcome evidence of President Clinton's readiness to involve the United States directly in the affairs of Eastern Europe. Not the least benefit of the deal will be to end Russia's fears of a hostile nuclear neighbour: the possibility, however remote, of a nuclear clash between Ukraine and Russia must rank high on any list of contemporary disaster scenarios.

The chief anxiety must now be that the agreement will be repudiated by Ukraine's nationalistic and heavily pro-nuclear parliament. At the very least, the deal will be hotly debated. Elections due in March could produce a yet more obstructive group of parliamentarians bent on retaining nuclear weapons as symbols of Ukraine's sovereignty.

Even more significant for the long-term security of Europe, if less tangible, was the nature of the language adopted towards Nato's enlargement to embrace former Warsaw Pact members. True, there is still no timetable for enlargement, no criteria and no formal naming of potential new members. All that is being offered is the halfway- house of the Partnership for Peace, an offer of military co-operation that is being extended to all and sundry, including Russia itself. But today's communique is expected to say that Nato 'expects and welcomes' new members, the more positive of two alternative formulas; and British officials have been suggesting that a timetable for the accession of the most eligible countries - Poland, Hungary and the Czech Republic - could emerge this year.

Vital though it is to give those countries the sense of security that they need for the full flowering of democracy, there is force in the argument that to act now would risk inflaming nationalist sentiment in Russia - hard on the electoral success of the extreme nationalist Vladimir Zhirinovsky and his so-called Liberal Democrats.

Only over the advisability of launching air strikes against the Bosnian Serb forces shelling Sarajevo did the alliance show its divisions. Those differences of opinion are understandable, given the potential dangers posed to the ground forces of Nato member states as well as to Bosnian civilians. Yet Western failure to stop the slaughter in Bosnia continues to challenge the logic of Nato's existence.