* Target for halting combat undercuts Taliban - Mattis
* Says security progress in Afghanistan "undeniable"
By Adrian Croft
LONDON, Feb 1 (Reuters) - A senior U.S. military commander said on Tuesday setting a 2014 goal for halting NATO combat operations in Afghanistan weakened the Taliban's arguments although he was "militarily uncomfortable" with it.
NATO agreed at a Lisbon summit last November to hand control of security in Afghanistan to Afghan forces by the end of 2014 and said the NATO-led force could halt combat operations by the same date if security conditions were good enough.
U.S. President Barack Obama has also said his aim is to halt major U.S. combat operations by the end of 2014.
Some critics argue that setting a target date plays into the hands of Taliban insurgents by encouraging them to wait out NATO forces.
General James Mattis, the head of U.S. Central Command which oversees the war in Afghanistan, said he was not concerned about the approach the United States was taking in Afghanistan "so long as it is done in concert ... with the allies".
In the short term, a target date may give the Taliban heart "to some degree", he said, speaking at an event in London hosted by the Policy Exchange thinktank.
But he said: "Having a conditions-based withdrawal is also a way to refute the enemy line that somehow we are there to occupy this country forever. I think there is actually a strength to it.
"Militarily, I'm uncomfortable with it, as all military men are, with the uncertainty, the unpredictability of war," he said.
"But we fight wars for a political reason. I hope we do. I hope we are not just fighting for the fun of it," said Mattis, answering questions after making one of his first major speeches since being appointed to the post last year. Some U.S. and NATO officials have said a spike in violence and problems in building up a capable Afghan army and police force to take over could make it hard to meet the 2014 goal.
Mattis said the Taliban and al Qaeda in Afghanistan were under the most significant pressure since the 2001 U.S.-led invasion "and we intend to keep it that way".
"The security progress is undeniable," he said.
"In key areas in Afghanistan the enemy is disoriented and on the defensive," Mattis said, although he said there would be very tough fighting ahead.
A mild winter in Afghanistan meant fighting continued in what was usually the "off season", he said. The U.S. Senate confirmed Mattis as new head of Central Command last August, replacing General David Petraeus, who took command of U.S. and NATO forces in Afghanistan.
Centcom, as it is known, oversees operations in a volatile swath of the world that covers 20 countries and stretches from Egypt across the Middle East and into south and central Asia. (Editing by Andrew Roche)
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