The Archbishop of Canterbury says he may yet regret not doing more to oppose the Iraq war.
Dr Williams always opposed the war
Dr Rowan Williams told BBC Radio 4's Today programme that taking a stronger position before the invasion may have made a difference.
The archbishop repeated his criticism of the decision to go to war, calling it morally and practically flawed.
This put the lives of troops at risk, he said, although he had no doubt the government had acted in good faith.
Asked whether he could have done more to express his concerns, he said: "I can't easily balance for myself the pros and cons" of whether to put himself at the head of a popular movement resisting the war.
"I said what I believed I needed to say. I shall need to think quite a long time about whether I could have said more, or less for that matter," he went on.
Watching the events unfold in Iraq had been deeply disturbing for him, he said.
BBC religious affairs correspondent Robert Piggott said the remarks showed that the archbishop felt a great responsibility as a moral leader to have intervened.
Dr Williams recently returned from a visit to the Middle East, and accused the UK government of placing Christians there at risk through its actions in Iraq.