More than 20 years after the end of the cold war, it might have been hoped that east and west would have developed new approaches to their residual quarrels. But no. Obscured by a cascade of more urgent events – chemical attacks in Syria, a tentative rapprochement with Iran and the devastating typhoon in the Philippines – a particularly nasty, and very old-style, dispute has been building inexorably between Brussels and Moscow. It concerns the future of Ukraine, and it comes to a head next week at the Eastern Partnership summit in Vilnius, Lithuania.

The language used on both sides is highly charged. Ukraine, it is said, faces its most fateful choice since it voted for independence from the Soviet Union in 1991. It must decide whether its future lies in the east (aligned once more with Moscow) or in the west (with the eventual prospect of EU membership). And it must decide now. The date, 28 to 29 November, in Vilnius is presented as a deadline; after an inconclusive EU foreign ministers' meeting on Monday, any decision is now likely to go to the wire.

The actual question that Ukraine faces is whether to sign up to enhanced trade arrangements that are being offered by the EU, or whether it accepts instead Moscow's project for what it calls a Eurasian customs union. Ukraine is not the only former Soviet-bloc state in this position. Initially, it was one of four. Armenia dropped out, opting for the deal from Moscow, while Moldova and Georgia are clear about wanting to orientate themselves towards the EU.

But of the four, Ukraine is the biggest, the most economically powerful and the most symbolic by far. And, of course, the dispute is not only, or even mainly, about trade. If Moscow "loses" Ukraine, so say advocates on both sides, it loses all pretence to be a great power. Ukraine is seen as crucial to President Putin's ambition to resurrect the Soviet Union as a free trade grouping, and if Ukraine bows to pressure from Moscow, is this not granting Russia a de facto policy veto, and then what price Ukrainian sovereignty?

Nor is the dispute just about Moscow's future clout. It is also about the EU. As current president, Lithuania hoped to make its mark both by effective diplomacy that would put this small, new EU member on the map, and by playing benevolent godfather to Ukraine, its much bigger neighbour. Ukraine's choice is also regarded as a token of whether the EU wants to, or even can, expand.

All these are reasons why the lobbying, from both sides, has been ferocious. Since the summer, scarcely a week has gone by without an envoy from one party or other, or from Ukraine itself, visiting London and other capitals to argue their case. There have been threats – veiled and not – from the west about allowing Ukraine to spin off forever into Moscow's orbit, and warnings from Moscow about the cold and lonely future that would be Kiev's if it were foolish enough to rely on the EU.

Russia, characteristically, followed up with some real intimidation, banning certain exports from Ukraine (and Moldova) on spurious health and safety grounds to illustrate the deprivations that might be to come. The EU has also queered Ukraine's pitch by making "selective justice" an issue – by which it mostly means the continued imprisonment of the opposition leader, Yulia Tymoshenko. "If it weren't her, they'd have found some other pretext to get at us," objected one piqued Ukrainian official.

But is this really how east and west should still be conducting their business, a generation after the Soviet collapse? Was it sensible to allow Lithuania's national dignity to become so entwined with an EU decision, and did Russia have to be so quick to deploy the trade weapon? Is there really no alternative to brinkmanship, all-or-nothing, and angry words?

At its most basic, the origin of this dispute lies in the supposed incompatibility of the EU's liberalised trade deals and Russia's customs union, which both Brussels and Moscow present as mutually exclusive. This confronts Ukraine with an impossible choice. With more time, would it really not be possible to negotiate transitional arrangements that entailed less of an either-or? After all, Russia is now in the World Trade Organisation and has long been quietly adopting many of the EU's regulatory standards. Somewhere there should be the seeds of a solution.

There is one reality, though, that cannot be, and should never have been, lost sight of in pursuit of what looks increasingly like an artificial deadline. Ukraine is united about being an independent state, but divided about its future direction. And while it is becoming less dependent on Russia, specifically for energy, Soviet-era trade patterns take time to unravel and, in agriculture at least, can operate in Ukraine's interests. Attitudes may change, but geography remains.

So fraught have preparations for the Vilnius summit now become that an EU failure to clinch the deal with Ukraine risks being hailed by Moscow – in time-honoured cold war fashion – as a victory. This is a short-term setback the EU may have to bear, before trying again for a less exclusive agreement that will require more time, and a lot less outdated ideology.