The US has said that it may rethink its plan to begin withdrawing troops from Afghanistan by July 2011 if conditions on the ground prevent a security handover to the Afghan government. Pressed on Wednesday by Republicans sceptical about fixing a timeline for withdrawal, Robert Gates, defence secretary, said that the strategy unveiled by President Barack Obama on Tuesday was narrower than past US objectives for Afghanistan and achievable within the timespan the president had set out. Mr Obama plans to send 30,000 extra troops to the country by the summer of next year and begin a pull-out of US forces a year later. Appearing at the US Senate with Hillary Clinton, secretary of state, and Admiral Mike Mullen, chairman of the joint chiefs of staff, Mr Gates sought to allay Republican and Democratic criticism of the planned troop surge and exit strategy. But his comments underlined the difficulty for the US in meeting Mr Obamas goal of turning around the eight-year Afghan war in eighteen months, and satisfying the presidents own party that the troop increase will not be a long term one. Our current plan is that we will begin the transition in local areas in July of 2011, he said. [But] we will evaluate in December 2010 whether we believe we will be able to meet that objective. If circumstances dictate in December the president always has the freedom to adjust his decisions. In a speech at West Point military academy in New York state, Mr Obama said he had decided the troop increase was in the USs vital interest because of the threat posed by Islamist extremism and deteriorating conditions on the ground. But some Democrats are worried about an escalating war. In a Gallup poll just before the speech, only 35 per cent of respondents said they approved of Mr Obamas handling of Afghanistan, with 55 per cent disapproving. On Wednesday, some Democrats signalled reluctant support for the strategy, with others expressing opposition. Republicans praised the troop surge but trained their fire on the exit strategy. A withdrawal date only emboldens al-Qaeda and the Taliban while dispiriting our Afghan partners and making it less likely that they will risk their lives to take our side in this fight, said John McCain, Mr Obamas defeated presidential rival. But he added: I support the presidents decision and I think it deserves the support of all Americans, both Republicans and Democrats. Mr Gates said the strategy set six goals. These included reversing Taliban momentum; denying the Taliban access to key population and production centres, and lines of communication; disrupting the insurgents elsewhere; and preventing al-Qaeda from restablishing itself. They also involved degrading the Taliban to levels manageable by Afghan national security forces, increasing the size and capability of the Afghan national army and police while also working with local forces and selectively building the capacity of Afghan government. Highlighting the scale of the task, Mr Mullen said Washignton believed the Taliban had achieved a dominant influence in 11 of 34 provinces.(FT)