Four large issues are involved in the current drive to develop a European Union military capability after the Kosovo war. They are difficult to define precisely, often the hallmark of important political transitions. Ireland faces major policy challenges on all four counts.

First there is the distinction between security and defence: what is this military capability for?

There is, secondly, a distinction between wars of choice and obligation: is a new military alliance being constructed in which all EU member-states will automatically be involved? Thirdly, there is the distinction between NATO and the EU: how will they relate to one another? - and what role will the United States have in the new relationship? Fourthly, there is the distinction between neutral and aligned states: does it make sense any more?

The purpose of the new military capability is set out in the Treaty of Amsterdam, where it is defined as "humanitarian and rescue tasks, peacekeeping tasks and tasks of combat forces in crisis management, including peacemaking".

This is a very broad agenda, but does not involve classical collective territorial defence based on mutual assistance guarantees. After the end of the Cold War the nature of security changed profoundly in Europe. It was extended to encompass a pan-European security community, a continental zone of peace.

The new military capability is designed to police this continental enlargement and its new peripheries through stabilisation and peace policies directed at common security, democracy, humanitarian intervention, environmental protection, support for minorities and the resolution of border disputes.

When prevention and peaceful co-operation fail, military capability becomes necessary. The rapid reaction force now under construction will need up to 250,000 troops available to give full cover, taking account of rotation, logistical and engineering backup. It is undoubtedly a major force; but it is directed to new and unprecedented tasks, in which Ireland is fully involved by virtue of political and economic interests in continental security and stability.

Military and security specialists increasingly make the distinction between wars of choice and obligation. The political formula agreed in the Treaty of Amsterdam makes participation in such operations voluntary on a case-by-case and activity-by-activity basis. Those who opt in have full political rights in directing them; those who don't, don't. That preserves the distinction between this rapid reaction force and collective alliance-based defence.

BUT given the transformation of European security arrangements, it not surprising that the new tasks are widely seen as permissive by such securocrats. The decision to set up the force at the Helsinki European Council last December is seen by them as a major turning point with long-term spillover effects. Many regard the assurance there that the force does not imply the creation of a European army as a political figleaf for the neutral and Atlanticist states. They also take it for granted that the large powers will operate as an informal directoire in its decisionmaking.

But they in turn probably underestimate political resistance to such a project, including the legal question of whether treaty changes are required to implement the new structures, to be decided at the Feira summit under Portugal's EU presidency on June 19th-20th.

A crucial issue in the current negotiations concerns relations between the new EU political-military structures and NATO. The six European non-EU members of NATO demand participation as of right because they say NATO assets and collective security guarantees may be triggered by the EU rapid reaction force.

Despite the commitment to create new EU intelligence, airlift and logistical capacities, it is universally recognised that NATO will not be displaced by the new structures. The US will remain the predominant military superpower for the foreseeable future, with a virtual monopoly on such resources.

Will it also have a right to be directly involved, based on its continuing fundamental interest in a transatlantic alliance? The EU's High Representative on security and foreign policy, Mr Javier Solana, proposes that there should be mutual joint participation in relevant committees.

That is resisted by the French and other governments.

The US Deputy Secretary of State, Mr Strobe Talbott, says cogently that his government "would not want to see a European security and defence identity (ESDI) that comes into being first within NATO but then grows out of NATO and finally grows away from NATO, since that would lead to an ESDI that initially duplicates NATO but could eventually compete with NATO".

There's the rub, the geopolitical conundrum at the heart of this transition. Paradoxically, Ireland's military neutrality has been preserved since the end of the Cold War by the persistence of British and other Atlanticist commitments to NATO, which resisted the development of an EU military capability.

Now that it is under way, Ireland has to choose, not as yet between neutrality and an alliance, but between isolationist passivity and voluntary engagement to preserve its influence at the rapidly developing core of the EU's political system.