Special forces like the SAS are to be boosted as part of a new military strategy to take on al Qaida and other terror networks that threaten Britain's security, Defence Secretary John Hutton is to say.
He will announce plans for a "major rebalancing" of the armed forces over the next 10 years.
It will give greater priority and investment to special forces units which are able to strike at terror groups "behind enemy lines".
The new strategy is prompted by a recognition that the old principles of deterrence which dominated military thinking during the Cold War are not applicable to the struggle against extremist terror.
The readiness of Islamist fanatics to carry out suicide bombings or to sacrifice children in ambushes on British troops has consigned traditional theories of deterrence to the history books, Mr Hutton will say.
In a speech, Mr Hutton will say that "deep and wide-ranging changes to our armed forces" are certain to result from an urgent analysis of lessons learnt from the struggle against Taliban insurgents in Afghanistan initiated by him and US Defence Secretary Robert Gates last month.
A major reassessment of military priorities is already being carried out by US President Barack Obama's administration in Washington, Mr Hutton will tell a conference of the Institute for Public Policy Research in London.
And he will add: "We need to see a similar readjustment here in the UK in the years ahead - a rebalancing of investment in equipment and people to meet the challenge of irregular warfare."
Mr Hutton will say that Afghan and Iraqi militants' use of tactics like female suicide bombers and boys tricked into pushing wheelbarrows of explosives up to British troops has "torn up the rule-book of traditional conflict".
The September 11 suicide attacks in the US and the July 7 bombings on the London transport network are "proof that traditional deterrents do not work against violent Islamist extremism", he will say.
