Britain's armed forces must prepare for a "generation of conflict", the head of the Army has said.
Gen Dannatt said the Army faced "extremism and jihad" in Iraq
General Sir Richard Dannatt's comments, released by the Ministry of Defence, were made to a Royal United Services Institute conference in June.
Gen Dannatt also warned of the threat from a "strident Islamist shadow" over the world and the need for "some form of success" in Iraq to combat it.
He said the Army was facing a global "conflict of values and ideas".
At the conference, which members of the media were not allowed to attend, Gen Dannatt said the Army had held discussions on how to prepare for the possibility of "a generation of conflict".
He said troops must have the right training and equipment, but should also be prepared for a much longer fight for "hearts and minds".
"The heady appeal of 'go first, go fast, go home' has to be balanced with a willingness and a structure 'to go strong and go long'", the general said.
'Extremism and jihad'
Gen Dannatt stressed the need for some progress in Iraq and "significant achievement" in Afghanistan.
"It is success today in these two theatres, however you define success, that, as far as I'm concerned, is both the top and bottom line because, if we fail in either campaign, then I submit that, in the face of that strident Islamist shadow, then tomorrow will be a very uncertain place," he said.
Gen Dannatt said Britain's mission in Iraq must be to help "construct a modern Islamic state in the tinderbox that is Iraq in the face of extremism and jihad".
He added in Afghanistan the Army was "on the edge of a new and deadly great game", referring to a phrase popularised by Rudyard Kipling.
The author used the term to describe the strategic battle between Britain and Russia during the 19th and early 20th Centuries.
Foreign Secretary David Miliband said he believed Gen Dannatt was referring to the UK's role in a long-term "military, diplomatic and ideological" battle against terrorism and extremism.
"Anyone who tells you there's a short-term fix in Afghanistan isn't telling you the truth," Mr Miliband told BBC Radio 4's Today programme.
Gen Dannatt also warned the high esteem in which the Army was held by British people was "fragile and under no circumstances must we take this for granted".
It "may be increasingly difficult to gain" the public's respect and trust, he added.
There are currently 5,500 British troops deployed in Iraq as part of Operation Telic.
Some 1,600 were withdrawn earlier this year and the government has said another 500 could leave by December if conditions are right.
In Afghanistan, there are currently about 7,100 UK personnel, mostly stationed in Helmand province. The MoD plans to increase that figure to 7,800 by October 2007.