* Shock 2013 defeat on Syria action hurt UK's reputation
* UK leader moving towards vote on joining U.S.-led strikes
* Cameron wants to prove Britain is engaged in world
* But sceptics say bombing not enough to defeat IS
By Kylie MacLellan
LONDON, July 22 (Reuters) - Prime Minister David Cameron may
have won an unexpectedly decisive election victory in May, but
he has yet to convince Britain's allies he is a globally engaged
foreign policy player.
Washington watched with alarm as Cameron presided over a
downgrading of Britain's military and diplomatic muscle during
his first term, culminating two years ago with his loss of a
crunch parliamentary vote to authorise air strikes on Syria.
"Our concern is a Great shrinking Britain," one senior U.S.
diplomat bemoaned recently.
Stung by such talk, Cameron is banking he can now convince
his country's parliament to vote to join U.S.-led air strikes on
Islamic State militants in Syria.
He calculates such a move - not expected until after the
summer - should re-establish his international statesman
credentials.
After fighting an unusually parochial election campaign, he
has begun to talk up his foreign policy ambitions, declaring at
a summit of world powers in Germany last month that Britain was
"back".
He then pledged to keep defence spending at NATO's target of
2 percent of gross domestic product, a policy he had initially
resisted committing to because of his desire to cut Britain's
sizeable budget deficit.
The memory of his humiliating 2013 parliamentary defeat over
taking military action against Syrian government forces - seen
internationally as a sign Britain was retreating from the world
- still rankles though.
"The damage it did was far and away greater than any of us
expected, and it has hung on this leadership ... he is trying to
distance himself from that embarrassment," Michael Clarke,
Director General of defence and security think tank the Royal
United Services Institute, told Reuters.
Clarke said the fact Cameron narrowly avoided presiding over
the break-up of the United Kingdom at last year's Scottish
independence referendum, and his demands for changes to
Britain's ties with the European Union ahead of a membership
vote, had also damaged his standing.
"His international reputation isn't that high ... so he has
got quite a lot of bouncing back to try to do," said Clarke,
adding that Cameron's pledge not to seek a third term means he
now has an eye on his legacy.
"He wants to personally restore his image as a world leader
of some importance, not (be seen as) the coalition prime
minister who presided over a retreat on all fronts."
NEW SITUATION
The political situation has changed since parliament's 2013
vote on Syria. Back then, Cameron was seeking approval to target
Syrian government forces in retaliation for their suspected use
of chemical weapons. U.S. President Barack Obama eventually
called off the strikes after Syria promised to give up its
chemical arsenal.
This time, the target is Islamic State, the militant group
that has seized swathes of Iraq and Syria, beheaded British
hostages and whose followers claimed responsibility for a
Tunisia attack in June in which 30 British holidaymakers were
killed. The government says it poses a direct threat to Britain.
The United States has been leading a coalition of Western
and Arab countries bombing Islamic State positions in both Iraq
and Syria since last year. Britain has sent jets to participate
in the bombing raids in Iraq, but not in Syria.
The limited role is a big change from Britain's position as
Washington's main battlefield ally under Cameron's predecessors
Tony Blair and Gordon Brown, when tens of thousands of British
troops served in Afghanistan and Iraq and more than 600 died.
That heavy cost has made the British public reluctant to
back new military action. But a YouGov poll this month found 57
percent of Britons would back the Royal Air Force joining
strikes in Syria, compared to 21 percent who were opposed.
Scarred by the events of 2013 when he recalled parliament
during the summer break for a rushed and ultimately unsuccessful
vote, Cameron is taking a more cautious approach at building
support this time.
Earlier this month, he invited senior opposition Labour
Party lawmakers to a national security meeting to be briefed on
the IS threat. He is not expected to push for a vote until after
Labour has elected a new leader on September 12.
"If we lost the vote again it would be game over for
Britain. The prime minister won't do it unless he is sure he can
win," said a senior government aide, describing Labour as
"sceptical but persuadable".
WAR FOOTING
Good will among lawmakers was dented last week however when
the Ministry of Defence disclosed that British pilots embedded
with U.S. and Canadian forces had already taken part in air
strikes in Syria without lawmakers' knowledge.
That prompted some politicians to complain that the will of
parliament had been ignored. Several lawmakers on Monday said
the government would need to do more to persuade them of the
merits of Britain extending military action to Syria.
"You can't take parliament with you if you keep parliament
in the dark," said Labour defence spokesman Vernon Coaker.
Defence Secretary Michael Fallon, who said it was illogical
to target IS in Iraq but not Syria, said the high precision
missiles Britain's Tornado aircraft fire was one of the reasons
its allies were keen for it to join the action in Syria.
Yet while bombing Syria may go some way towards resurrecting
Britain's global clout, U.S.-led forces are hardly short of
firepower, and the addition of British aircraft is not likely to
make a major difference to the mission.
Critics say gains by Islamic State in both Iraq and Syria
show the limits of the U.S.-led strategy of bombing from the
air, and that Western ground forces may be needed.
Cameron and Fallon have repeatedly said there is no question
of British "boots on the ground".
But David Richards, former chief of Britain's defence staff
and commander of international troops in Afghanistan, said the
issue of British ground troops would need to be revisited if no
progress was made in the next year.
"The current strategy is essentially one of equipping and
training others to do the hard stuff for us. I think that could
work, but the scale of effort going into it is woefully
insufficient," Richards told the BBC's Andrew Marr show.
"If you really want to get rid of them, we need to
effectively get on a war footing."