UN rapid reaction forces were used in Bosnia
Proposals for a European rapid reaction force are on the agenda in Laeken, Belgium, where EU leaders will also hold talks on anti-terror measures and plans for a peacekeeping force in Afghanistan.
Shadow defence secretary Bernard Jenkin has renewed the Conservative assault on plans for a common European defence and security policy.
That attack was rebutted by Foreign Secretary Jack Straw, who cited the international coalition's success in Afghanistan as an example of how effective military cooperation could be.
The Conservatives fear the new European force could undermine Nato.
Policy confusion
Speaking on BBC Radio 4's Today programme, Mr Jenkin said: "The strength of Nato is that it's purely a military alliance. It does not purport to have a foreign policy or citizenship or a currency or to make laws in its member states.
"The problem of an EU foreign and defence policy is all these other problems are going to get caught up with the price of fish."
The Tory spokesman warned the move was primarily about politics, not security.
Mr Straw instead argued a European force would compliment Nato, whose assets it would use for missions where America did not want to be involved.
"This is not about a European super-state of any of that nonsense," the foreign secretary told Today.
"What we have shown through Nato is that it is possible to add value to what nation states alone can do by pooling sovereignty."
Mr Straw said the campaign in Afghanistan had been a success for US leadership but also for the United Nations, which had given the operation legal authority.
Tackling instability
But the EU itself needed to develop rapid reaction forces.
"There is no doubt that for the future, as we have seen over the last 12 years since the breakdown of the Berlin wall, there are going to be many more occasions where there is going to be political instability.
Mr Straw is joining the prime minister at the summit, where Downing Street says Mr Blair will discuss plans for a security force in Afghanistan with the other 14 EU leaders.
The summit comes as senior military figures from the international coalition hold talks in London on how such a force would work on the ground.
Downing Street says the UK would be prepared to lead such a force.
'Chilling' words
The latest moves to secure peace in war-torn Afghanistan follow the US release of a video showing Osama Bin Laden joking and boasting about the US terror attacks.
Mr Straw said there was no doubt the tape was genuine and argued it was further vindication of military action to root out a man who "revelled in death and destruction".
"People are able to see Bin Laden there with these chilling words of admission about his guilt in organising the atrocities on 11 September," he continued.
The key debate at the summit will come on Saturday when the leaders look at how to reform various EU institutions.
How to change the union's constitution to accommodate new members is likely to form part of those talks.
Plans for a Europe-wide arrest warrant are also expected to be approved at the summit as part of the wider clampdown against terror groups in the wake of the 11 September attacks.