* Britain prepares for possible Afghan troop increase
* Cost of failure would be enormous, British army chief
WASHINGTON, Sept 22 (Reuters) - Britain is readying plans to deploy more troops to Afghanistan should Washington pursue a larger ground campaign, as advocated by the U.S. and NATO commander there, the British army's commander said on Tuesday.
General David Richards, who took over as chief of the general staff last month, said an increase beyond the about 9,000 British forces in Afghanistan was a "prudent anticipation of what might be required."
"It is not an absolute nor a given at this stage," he said during a visit to Washington, in comments confirmed by his spokesman.
The Times of London reported Britain might deploy up to another 1,000 troops to Afghanistan.
Richards spelled out the importance of succeeding in Afghanistan in an address to a Washington think-tank, saying: "We can redefine success, but we need to succeed in Afghanistan."
Army General Stanley McChrystal, the top commander of U.S. and NATO forces in Afghanistan, warned in a confidential assessment leaked earlier this week that without additional troops the mission would "likely result in failure."
But U.S. President Barack Obama described himself in weekend interviews as a "skeptical audience" when it came to deciding whether to send more troops, and NATO allies could be an even harder sell.
U.S. public opinion has turned against the war, combat deaths have risen, and analysts doubt that European allies will make any significant further contributions unless they are part of a clear plan for training Afghan security forces.
MORE AFGHAN TRAINING
British Prime Minister Gordon Brown has repeatedly emphasized the need to "Afghanistanize" the conflict -- training more Afghan soldiers and police to take on the task of providing national security.
Britain has lost 216 soldiers in Afghanistan -- exceeding the total who died in the Iraq war.
But Richards cautioned that the cost of perceived failure would extend well beyond Afghanistan. It could restore sanctuary to al Qaeda and raise the risk of terrorist attacks in Western nations.
"Add to that the hugely intoxicating impact on extremists worldwide of the perceived defeat of the U.S.A. and NATO, the most powerful alliance in the history of the world," he said.
"Anything ... might be possible then in the extremist eyes."
The White House has put off consideration of sending more troops to Afghanistan while it assesses whether its war strategy can still work and after a flawed election that cast doubt on the Kabul government's legitimacy, officials said on Tuesday.
Richards, a former NATO commander in Afghanistan who recently returned from a visit there, said it was important to give Afghan President Hamid Karzai a chance, should his re-election be confirmed.
"President Karzai does understand that we're all watching, that we want him to succeed if he's confirmed. But you know, how he goes about it now is so important and he's very, very alert to that," Richards said. (Editing by Deborah Charles and Philip Barbara)
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