* UK cutting defence spending 8 pct over five years
* Thinktank sees combat capability down 20-30 percent
* France seen more militarily assertive
* Defence chief warns of "strategically incoherent" force
By Peter Apps
LONDON, Feb 9 (Reuters) - As British troops strip down equipment and load containers to leave Afghanistan, its military self-confidence has rarely been lower.
When Britain ramped up its presence in Helmand Province in 2006, it was a different story.
Afghanistan, current and former officers say, was seen as a winnable war that would showcase Britain's military and rebuild its reputation with U.S. officers underwhelmed by its performance in Iraq.
Both inside and outside the armed forces, however, the recent campaign is increasingly seen as a disastrous error, seriously sapping Britain's enthusiasm for using military force just as savage budget cuts begin to bite.
Other Western allies are cutting their budgets too. However the bottom line for Britain, analysts say, is that it may simply be left without the forces or the will to mount operations as it has in the past.
Last month former U.S. Defence Secretary Robert Gates complained Britain's military could no longer offer a "full spectrum" of military capabilities to act as a full U.S. ally in future conflicts or confrontations.
That prompted an angry rebuttal from Prime Minister David Cameron, pointing to new equipment purchases. Britain will launch the first of two new aircraft carriers later this year, having spent several years with none. Defence sources say its first order for more than a dozen F-35 Joint Strike Fighters could come within weeks.
Even within Whitehall, however, there is open debate over the military's focus.
In a speech to the Royal United Services Institute in December, Chief of Defence Staff General Nicholas Houghton said that concentrating too much on "exquisite equipment" risked leaving a "hollow force" with inadequate personnel.
"Unattended, our current course leads to a strategically incoherent force structure," Houghton said.
He said that while in his 40 years of service the military been never been held in such high public regard as it is now, "the purposes to which they have most recently been put have seldom been more deeply questioned."
Recent wars, he said, had produced a "creeping reluctance" to use force that could prove problematic. Britain lost 447 soldiers in Afghanistan - twice the losses in Iraq or the 1982 Falklands War.
In September, when Parliament vetoed British involvement in any U.S.-led strike on Syria, many officials saw the move as setting a precedent that could also limit future operations.
London's International Institute for Strategic Studies (IISS) estimates that the eight percent planned cuts in defence spending from 2010 would reduce Britain's combat capability by 20-30 percent.
On Wednesday, the IISS's annual global military balance assessment showed Britain has lost its place as the world's largest defence buyer to Saudi Arabia, although it remains the largest in Europe outside Russia.
France might have a lower overall defence budget - $52 billion in 2013 against Britain's $57 billion, according to the IISS - but it is increasingly seen to have greater military reach and enthusiasm to act.
A Pentagon-funded report by the U.S.-based Rand Corporation said France had built a more flexible military able to adapt more quickly to conflicts like in Libya or Mali. By comparison, Britain's focus on Afghanistan had left its army "too bespoke" and ill-suited to other conflicts.
In the words of one UK defence source, the British military "is now perfectly designed to support the U.S. in the kinds of wars America has no intention of fighting again."
Nor is that the only worry.
"The Syrian vote was a big deal," says Nikolas Gvosdev, professor of national security studies at the U.S. Naval War College. "We had always assumed Britain would be there and then suddenly it wasn't."
A new strategic defence review is expected in 2015, also the year of Britain's next general election.
Interservice rivalries, some say, have long bedevilled British defence planning, as has a political focus on retaining defence industry jobs in marginal constituencies.
In addition, Scotland - home to Britain's nuclear deterrent submarines - will be voting in a referendum this year that could see it secede from the United Kingdom, although most polls suggest it will not. Cameron's promised vote on Britain's membership in the European Union could also have an impact on military relations with European powers, particularly France.
With garrisons in Germany closing, a larger majority of Britain's army will be based within its shores than at any time since the 18th century.
On paper, Britain's "Force 2020" - the military it expects to have by the end of the decade - should be able to provide one ongoing "stabilisation operation" with up to 6,500 personnel, ships and aircraft, together with shorter-lived operations with 1,000-2,000 troops.
The largest single one-off operation the military could mount, the Ministry of Defence said, would involve some 30,000 personnel, roughly two-thirds of its 2003 Iraq force.
However, defence experts say that assumption was based on no further cuts - something seen as relatively unlikely.
Britain's military is still broadly respected. Its special forces remain legendary - if small - and the Royal Navy's 15-ship minesweeper force is amongst the world's largest, much of it permanently deployed to the Gulf where U.S. commanders say they would prove vital in any war.
The new carriers - although the second may yet be mothballed - will be the largest warships Britain has ever launched, potentially valuable to U.S. and other allies as their overstretched navies struggle to cover the globe.
Still, defence chief Houghton warned the Royal Navy in particular risked losing "critical mass" in personnel.
In January, British media reported the country's only available warship was forced to sprint the length of the North Sea at maximum speed after a Russian warship began loitering near UK territorial waters off Scotland.
A smaller military is not necessarily less capable. Britain might now have only 230 fast combat jets against 450 in 1993, but they are much more capable, able to launch Storm Shadow cruise missiles without even entering enemy airspace. British defence technology is still seen as world-class.
There is also no shortage of enthusiasm for new tasks. Houghton said he favoured increasing the number of troops on U. N. peacekeeping and others talk of increasing training missions to Africa.
Finding those troops could be tough, however. The army will take by far the brunt of impending cuts, losing 20,000 soldiers from 2010 numbers to stand at 82,000 by 2018.
Plans call for reserve forces to grow from some 22,000 now to 35,000 by the end of the decade. But recruitment has so far been lacklustre at best, and the number of part-time soldiers has actually fallen, according to the MoD's latest quarterly report. A new recruitment campaign has begun.
Britain's fourth Anglo-Afghan war looks set to end better than the first, an initially successful 1839 invasion that turned into outright defeat and disastrous withdrawal three years later.
However critics say that by going on the offensive in Helmand in 2006 Britain may have made matters in Afghanistan worse, helping kickstart a nationwide insurgency. The operation was launched when a UK general, David Richards - later head of the entire British military - was commanding the NATO force.
U.S. officials were also unimpressed after a September 2012 attack on the UK-guarded Camp Bastion killed two U.S. marines and destroyed several aircraft. The Pentagon fired two U.S. generals shortly after but no British officers were punished. The MoD says there was no evidence UK commanders were responsible.
"The irony is that Afghanistan was supposed to justify the Army's existence," said one former officer on condition of anonymity because he was still involved in defence policy. Instead, "it's ended up guaranteeing its destruction." (Editing by Sonya Hepinstall)