Whoever Ban picks, the choice is unlikely to cause a stir in Brussels, just as the recent reshuffle of European Commissioners hardly set the UN abuzz. Bureaucrats working for one international organization are usually blissfully unaware of what goes on in another.

But this is one UN job offer that EU-watchers should take notice of. Although the head of peacekeeping is technically on a par with the official in charge of conference services, he has the potential to influence not only UN missions but EU security cooperation.

Although most commentators on the European Security and Defence Policy (ESDP) focus on how it fits in with NATO, it has grown up hand-in-hand with UN operations.

During Jean-Marie Guéhenno's time in office, UN peacekeeping has expanded at a rate that he could not have foreseen. In mid-2000, the organization had just more than 12,000 personnel in the field – memories of Srebrenica and Rwanda remained strong. But international efforts to end a series of bloody African conflicts, combined with fast-moving crises from Haiti to East Timor, fuelled demand for a new wave of peacekeepers.

Today the UN has over 90,000 soldiers and policemen deployed worldwide – one and a half times as many as NATO. The number is expected to hit 110,000 by the year's end.

Western analysts take a dim view of UN forces: heavily reliant on Asian and African troops, they are low-tech and do not match visions of twenty-first century warriors.

Yet these are often the only forces available for trouble-spots like Liberia, the Democratic Republic of Congo and Darfur. And so they keep on being deployed. The UN's peacekeeping budget has reached $7 billion a year, two-fifths of it paid by EU members.

But the EU's support for the UN is not solely financial. The European Council has mandated a series of ESDP operations to work alongside the UN, ranging from emergency military interventions (such as 2003's Operation Artemis in the eastern Congo) to smaller-scale police training missions. Outside Europe, there is currently not one ESDP operation that is not co-deployed alongside some form of UN presence.

It's hard to imagine ESDP having got anything like as far as it has without the UN as a partner. The UN and EU are the Obelix and Asterix of international security: one handling big, slow missions while the other concentrates on smaller, flexible, operations.

A quick survey of 2008's top European security stories so far brings home how closely the two organizations are intertwined. In Kosovo, EU and UN officials are attempting a smooth transfer of policing responsibilities. In Chad, UN police are deploying to support the largely French military force trying to secure refugee camps bordering Darfur. And in Afghanistan, the appointment of a new UN Special Representative – Norway's Kai Eide – has been presented as the last best chance to sort out NATO's faltering mission.

So while the only large blue-helmeted mission involving significant European contributions is in Lebanon, the fate of UN peacekeeping is directly relevant to the EU. Paris has put up a strong fight to ensure that Guéhenno should be replaced by another Frenchman – the US, noting peacekeeping's significance, also had its eye on the job.

But it's not a job that anyone would take on lightly. Impressive as the UN's expansion has been, it is now looking overstretched. It has struggled to find the helicopters and transport units it needs for Darfur, now its highest-profile mission. In private, UN officials fear that under-equipped peacekeepers risk stumbling into another Srebrenica.

And while EU-UN relations have proved important for both, there is still a great deal of improvisation: planners admit that cooperation on the joint mission in Chad has actually been less effective than in some earlier cases. While the EU military force there is meant to hand off to UN troops after a year, it's far from clear if the latter can be ready in time.

So ensuring that a European sits at the top of the UN peacekeeping pyramid is not enough. As the UN's leading donor, the EU needs to investigate how to ensure that UN missions get the high-end assets, like helicopters, that it needs in a place like Darfur.

France and Britain recently suggested creating a pool of helicopters for NATO and EU missions – it should be possible to do something similar for the UN, and at lower cost.

And as the UN's frequent operational partners, the EU and NATO should develop more structured joint planning procedures for future missions (these should be open to other peacekeeping players, like the African Union). They could also develop a joint action plan to provide the UN with urgent logistical and intelligence support in future crises.

And they might undertake a common assessment of likely trends in demand for peacekeepers over the next decade. These projections would give clues not only to the next phase in the UN's evolution, but also to what ESDP may look like in ten year's time.

The author is Associate Director for Policy at the NYU Center on International Cooperation, and UN Policy Fellow at the European Council on Foreign Relations.