FOCUS: WAR IN EUROPE: Diplomacy staggers out of the rubble

f a week is a long time in politics, 36 hours is an eternity in war. On Thursday afternoon, the West achieved its biggest diplomatic success since the Kosovo conflict began, drawing Russia into the outline of a deal which could force Slobodan Milosevic to his knees. Late on Friday night, an errant Nato missile scored the most devastating own goal imaginable - a direct hit on the Chinese embassy in Belgrade.

At a stroke the painstaking feat of the diplomats had been at the least imperilled, conceivably reduced to as much rubble as China's mission. The war that, after almost seven weeks, had seemed to be gaining a purpose, now appeared to be back to bombing for bombing's sake. Almost 200 extra American warplanes are being sent to the front line, in furtherance of an implausible strategy of blowing up power stations, bridges (and now foreign embassies) in the name of saving a province in the south of Yugoslavia that had already been reduced to an almost uninhabited wasteland.

In Nato capitals and on the floor of the UN in New York, the diplomats and politicians who should have been concentrating on building a watertight accord with the Russians have been forced to devote their energies to apologising. And not just for the debacle at the Chinese embassy. Obscured by yesterday's diplomatic pandemonium was the small matter of the cluster bombing which killed a dozen people in a residential area in Nis, the third largest city of Yugoslavia. This is, however absurdly, supposed to be a "humane" bombing campaign. But for the distraction of the embassy hit, more people might have asked why Nato was using cluster bombs designed to terrorise and kill people - and not on a battlefield, but close to a densely populated civilian area.

Nato now can only hope that indignation at its dreadful blunder will quickly subside, allowing the diplomatic process to resume. That may yet happen. But the process was never going to be simple. The agreement in principle reached in Germany by the foreign ministers of the Group of Seven leading Western powers and Russia is merely a road map to a settlement, which omits a host of hazards along the way. It could be several weeks before a detailed offer is ready to present to President Milosevic. Nonetheless, the satisfaction etched on the faces of Robin Cook and his colleagues on Thursday as they left the imposing Petersberg residence, high above the Rhine near Bonn, was justified.

It is not because they possess nuclear weapons, or because they might join the war on Yugoslavia's side, or because they are the one country Mr Milosevic listens to, that the Russians matter in Kosovo. They matter because they hold the key which opens the door to UN involvement in the crisis. From the outset it was clear, even to Nato hawks such as Britain, that a lasting Kosovo settlement could only come under the aegis of the UN. That, however, meant heading off the threat of a Russian veto in the Security Council.

In principle, the G8 deal has done this. The road map no longer points to endless Nato bombing, followed by a creeping occupation of Kosovo, of dubious international legality. Instead, a copper-bottomed UN resolution beckons, perhaps within two weeks. If Serbia is to lose Kosovo, Russia as well as Mr Milosevic would far prefer to lose it to an "interim" mandate of the UN than to a de facto Nato protectorate.

But now everything is more uncertain. The real question is not the destination, but whether the road to it is passable. Petersberg was a major setback for Mr Milosevic. If he had banked on using the Russians as a diplomatic shield against the need to make concessions, he had miscalculated. The reasons for the Russian shift were equally clear. Virtually isolated in its previous support for Serbia, Moscow would have had scant chance of securing the international financial aid it so desperately needs, had it persisted in blocking progress.

Far less clear was whether the price of getting the Russians on board was too high - whether unity on the Security Council perforce means a fudge that lets President Milosevic off the hook, and hands Nato a "victory" that is really a defeat. The strike on the Chinese embassy has redoubled these uncertainties. Russia may be less inclined to co-operate, and now Peking's veto power on the Security Council is a factor which must be taken into account. Even harder to quantify is the effect on public opinion; conceivably, Friday night could contribute to a fatal undermining of support for the war.

The details too will be tricky, none more so than the make-up of the peacekeeping force that will move into Kosovo and shepherd 700,000 or more returning refugees. By speaking of "effective international civil and security presences", the foreign ministers left the question open. But a gulf remains between the positions of the two sides. Though the alliance agrees that the force may be designated a UN force, it is adamant that at its heart must be Nato troops, wielding heavy Nato firepower, working within an exclusively Nato command structure. "As long as that's understood, it doesn't matter what we call the force," a senior alliance diplomat says, citing the example of the SFOR contingent, UN-wrapped but Nato-filled, which has kept the peace in Bosnia for four years.

From Belgrade, however, there have been only hints of acknowledgement that an armed international force is inevitable - and not the slightest sign that a single Nato soldier should be allowed in its number. Igor Ivanov, the Russian foreign minister, said on Thursday that Yugoslavia must approve the composition of whatever force does move in, an indication perhaps that Moscow's conversion to Western arguments is less than complete. And that was before the Chinese embassy strike.

All hinges on the fudge word "effective", apparently inserted by Mr Cook to ensure an agreed outcome. But when the drafters start writing a UN resolution and its detailed annexes, the issue will have to be confronted. Mr Cook and Mr Ivanov were to have met in Edinburgh this weekend, and might have sorted it out, but the bombing in Belgrade has blown their talks away.