AS the United States prepares for a troop surge in Afghanistan in the new year, Robert Gates, the defence secretary, and senior commanders are concerned that the British government lacks the “political will” for the fight.

General John Craddock, the Nato commander, said last week that Britain must put more troops into Helmand province to defeat the Taliban insurgency.

In an interview with The Sunday Times at Nato’s supreme headquarters in Mons, Belgium, he said Gordon Brown’s announcement last Monday that more troops would bolster Britain’s 8,100-strong force in Afghanistan by March was not enough. Although planning is under way to send up to 3,000 extra troops to Afghanistan next summer if required, Brown committed only 300 in his Commons statement.

“I don’t think 300 more, if you are talking about Helmand province, will do the trick. We’ve got to hold down there until we’ve got some Afghan street forces who can take over,” Craddock said.

Brown’s decision to pull out of southern Iraq - leaving US troops to fill the gap - and his reluctance to commit to sending a substantial number of extra troops to Afghanistan have rung alarm bells in Washington.

US defence chiefs are concerned that Brown would rather pander to war fatigue back home than provide the long-term forces necessary for the new anti-Taliban surge. They fear the deteriorating situation in Afghanistan could soon make the war there as unpopular with the British as the conflict in Iraq.

Air Chief Marshal Sir Jock Stirrup said last week that Britain would be able to redeploy some troops from Iraq to Afghanistan in the short term, but was ill equipped for a long fight. “We cannot just have a one-for-one transfer. The net result must be a reduction in our overall operation campaign,” said the defence chief.

A senior American defence adviser said Gates and US commanders were frustrated by the British response to their request for help. “They’re looking at the British government pulling out of Iraq and wondering, ‘Do they have the stomach for Afghanistan?’ Gates is concerned about the level of resources needed and the lack of political will to reinforce them.”

The US defence secretary has spelt out in a forthcoming issue of the journal Foreign Affairs that the mission in Afghanistan “poses an even more difficult and long-term challenge than Iraq - one that, despite a large international effort, will require a significant US military and economic commitment for some time”.

The Bush administration has prepared a classified review of Afghanistan due to be presented soon to the national security team of Barack Obama, the president-elect. It presents a series of “options” for the new administration, including the threat to withhold aid to Pakistan unless its military takes effective measures against militants in the Afghan border region.

Plans to increase US troop levels by 20,000 to 30,000 in Afghanistan are under way, Admiral Mike Mullen, chairman of the joint chiefs of staff, said last night. The strategy proposes to secure up to 40 “critical districts” - offering protection to the local population, coopting tribal militias and pouring resources into reconstruction and development. It is a continuation of the “clear, hold and build” strategy that has brought relative stability to Iraq.

“In Helmand, we’ve got to have a sharper effort in the coordination of ‘hold and build’. If there’s a shortfall, it’s in the funding and monies available for the military to do that,” said Craddock.

The Nato commander refused to put a figure on how many US and Nato troops were required. “We still have gaps; we still have key shortfalls, such as helicopters. We’re short of medium and heavy lift; we’re short of medivac [medical evacuation] . . . we’re short of intel [intelligence], surveillance and reconnaissance capabilities, so we need that filled up,” Craddock said.

John Nagl, a retired colonel who under General David Petraeus co-wrote the US army’s new counter-insurgency manual, said the extra US troops promised by the Pentagon would be a “good start”. However, he added that more international troops were needed to secure the local population while the national Afghan army was expanded and trained as a credible fighting force.

“The British nation has a decision to make about how important it considers Afghanistan to be,” Nagl said. This summer he attended a US seminar on counterinsurgency in which the British performance in Iraq was heavily criticised.

Daniel Marston, a US defence expert who has been embedded with British troops, said US forces resented the way the British had flaunted their supposedly superior counterinsurgency skills at the beginning of the war.

“Things [are] getting better because the British are recognising that they made mistakes and they were arrogant,” Marston said at the talk.

A senior defence adviser said relations between US and British military commanders had improved greatly.

General Sir Mike Jackson, the former chief of the general staff, said last night that the violence in postwar Iraq was “much exacerbated by the security vacuum created by Washington’s appalling decisions” to disband the Iraqi security forces. Removal of Saddam Hussein’s civil service loyalists had doubled the time coalition forces had to remain in Iraq.

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