When EU leaders sit down together in Cologne on Thursday they will be confronted by a most unusual subject for an EU summit.

A major debate will be dominated by the security and defence of Europe, both short-term and long-term. It is a discussion that usually takes place elsewhere.

Talk of Kosovo, and the EU's ambitious plans for a stability pact for the post-war Balkans, will be complemented by an ambitious reflection on how to develop what has been called Europe's new security identity.

In essence they will discuss how, instead of relying on US leadership, the EU can assume military responsibility through NATO for peace in the whole region.

The leaders will also fill the Union's new post of head of Common Foreign and Security Policy. The current Spanish Secretary General of NATO, Mr Javier Solana, is clearly heading the field followed by the outgoing Dutch External Relations Commissioner, Mr Hans van den Broek.

The former Tanaiste, Mr Dick Spring, mentioned at one time for the post, is no longer seen as a contender.

Kosovo has given the defence debate a new impetus, indeed an imperative, which the Irish political class would do well to acknowledge. Is it imperialist adventure or genuine humanitarian response, of which we should be fully a part, to the failure of global collective security?

But the road we are heading down has been well signposted. The Amsterdam Treaty gave the Union its first military dimension, strictly confined to a peacekeeping, peace-enforcing and humanitarian role, known as "Petersberg tasks".

To accomplish these tasks, the EU would borrow assets from NATO through the Western European Union (WEU), incorporation of which into the EU has been raised as a possibility.

Since then the EU, WEU and NATO have been talking about how this would work in practice. The discussion culminated in an important acknowledgement at NATO's 50th anniversary summit in Washington last month of the organisation's willingness to facilitate EU-led operations.

In November, in a major declaration at St Malo, Britain and France also pledged to enhance the Union's military capabilities.

Since then there has been much speculation about how to do that, ranging from incorporation of the WEU to its abolition and the devolution of its functions either to NATO or to the EU. The debate is about how to give real teeth to an EU Petersberg capability by going beyond the Amsterdam treaty.

However, politicians do not make history in conditions set by them, but in those inherited from the past.

When NATO's EU members established the WEU, in effect a bridge between the two organisations, they mirrored many of NATO's treaty provisions in its smaller sister organisation. Most notably, the core Article 5 of the statutes of both organisations commits member-states to come to the defence automatically of other member-states if attacked.

No one, however, ever really imagined that the WEU, largely until now an ineffective talking shop, would ever be called on to enforce such a guarantee. That was always a job for NATO.

Yet any suggestion of a merger between the WEU and EU is confronted immediately with this redundant obstruction, the diplomatic equivalent of the human tonsils.

Any merger involving full incorporation of Article 5 would be impossible for the neutrals because they define their neutrality by reference most simply to a refusal to be party to such an automatic undertaking to defend others.

Ironically, a merger without an Article 5 commitment would probably be unproblematical for the majority of the neutrals and yet the NATO member-states, despite retaining their ultimate protection under NATO's own Article 5, still refuse to contemplate its abandonment in the WEU.

The result is that the two substantially different issues, collective territorial defence and peacekeeping, will continue to be inextricably entangled.

Yet the Germans are keen, backed by the Italians, Belgians and Luxembourgers, to keep pressing the merger issue.

The neutrals - Ireland, Sweden, Austria and Finland - are not alone in urging a softly, softly approach which would not prejudge the issue.

The British and French also ask why this hurdle should be crossed at this stage when it is still a theoretical problem. They argue that instead of grandiose institutional reforms, the Union should concentrate on incremental changes which could enhance its practical capacity.

Such issues, London argues, could include developing an independent European heavy-lifting capability for troops and armour, greater co-ordination in armaments development and purchasing, or simply giving the Union the capacity to take military decisions.

Senior British sources warn of the danger of "rushing" the neutrals, now more often known as the "non-aligned", who, they say, are engaged in a period of slow soul-searching. And they are also concerned that a full merger would pose problems for states such as Turkey which are NATO, but not EU, members and want to be part of European security discussions.

The draft paper prepared by the Germans for the Cologne summit, and which has been seen by The Irish Times, raises problems for the advocates of a slower approach.

Most accept the inevitability of the establishment of a politico/ military committee in the Union to assess the needs and possibilities of military action. Currently any proposal for military action of even the most limited kind must go for assessment to the WEU, because the EU simply does not have the know-how.

The paper also suggests the establishment of an EU military staff and a situation centre. But diplomats make clear that such structures would be aimed at enhancing the decision-making and planning capacities of the Union rather than commanding troops in the field, which is a task for NATO or national commands.

The paper goes further in trying to set out a deadline of the end of next year for proposals on a merger of the EU and the WEU, assuming the inevitability of such a merger.

It also assumes that Article 5 of the WEU would also be incorporated into the EU in any such merger, albeit only for those who are members of NATO. The problem is that such a merger would inevitably then create two tiers of EU members, which Irish and neutral diplomats would strenuously resist.

Any proposals for an enhanced EU defence dimension, the neutrals insist, must provide for equality between the member-states.

Critics of the German proposals are also worried about creating a council of defence ministers within the EU, preferring to allow the general affairs council of foreign ministers to invite their defence counterparts to attend occasionally.

The outcome of Cologne may become slightly clearer after today's meeting of foreign ministers, but diplomats expect the summit to do little more than express general aspirations and pass the ball on to the incoming Finnish presidency.

Progress at the Helsinki summit in December will certainly be informed by the Finns' sensitivity to neutrals' aspirations. But movement there will undoubtedly be towards giving the Union a real military capability.