Blair also said the UK should keep its alliance with the US strong.
He reiterated that he believed it was "ludicrous" to suggest removing Saddam Hussein or the Taliban had inflamed Muslim opinion.
"Terrorism can't be defeated by military means alone, true. But it can't be defeated without it"
British Prime Minister
Blair also said that 24-hour media coverage complicated the task politicians faced persuading voters that these battles were worth fighting.
"Public opinion will be divided, feel the cost is too great, the campaign too long ... They will be constantly bombarded by the propaganda of the enemy, often quite sympathetically treated by their own media, to the effect that it's really all 'our', that is, the West's fault," he said.
Blair's support for the US-led invasion of Iraq has proven deeply unpopular at home where there is also concern over mounting British casualties in Afghanistan.
He has also faced criticism from British military commanders who say their forces are under funded and overstretched.
Blair acknowledged Britain would have to make new commitments to its armed forces if it continues its military policies.
"On the part of the military, they need to accept that in a volunteer armed force, conflict and therefore casualty may be part of what they are called upon to face," he said.
Blair has said he will step down later this year.