Having observed the destructive force of the terrorists in New York, which left him "extremely shocked", Dr Williams said great thought and effort should be applied to countering international terrorism.

Clergyman at the Church in Wales Governing Body meeting, Lampeter

He warned that any act of punishment for the attacks must not take the shape of revenge.

Five thousand people - including up to 300 Britons - are thought to have died in New York and Washington.

In his address, the archbishop will say: "No 'Star Wars' shield of missile defence could have averted last Tuesday's atrocities.

"No intensive campaign to search and destroy in Afghanistan will guarantee that it will never happen again.

"If we fear and loathe terrorism, we have to think harder.

"When those who have power respond with enormous threats and high rhetoric of relentless pursuit, they too are dealing with the anger of helplessness.

Indiscriminate terror is the weapon of the weak, not the strong

Dr Rowan Williams, Archbishop of Wales

"Last Tuesday's events were terrible for the USA - the US government had to struggle to overcome the sense of impotence in the nation.

"Indiscriminate terror is the weapon of the weak, not the strong; it's commonly what the 'strong' aren't expecting, which is why they are vulnerable to it.

"It is the weapon of those who have nothing to lose.

"If we want it not to happen, we have to be asking what it means that the world has so many people in it who believe they have nothing to lose.

His speech continues: "Today it is right and proper that we seek for justice.

Rt Rev John Davies: Appeal for calm

"Even in the extremity of anger and misery, people are always answerable for the choices they make, and the decision to kill several thousand innocent people was a real decision, an unspeakably wicked and deluded decision."

Archbishop Rowan will add: "So the challenge before the USA and its allies today, is to ask what is to be done beyond punishment to make any such punishment more than revenge.

Dr Williams will tell delegates in Lampeter that faith meant dealing with the fear of death.

"Last Tuesday, I was privileged to know for a couple of hours what it might be to face death in company, and was blessed with a group of people around me with whom I can say without exaggeration I was glad to be in such a moment.

The archbishop concludes: "We have to prove that risk and reconciliation are indeed 'a new and living way' and to plead with the powerful to consider where true security lies, lest the trap of violence close still more finally on us.

"It is a hard moment; perhaps we can understand afresh why we pray not to be brought to the time of trial and to be delivered from evil."