The Pentagon is probably underestimating the future cost of fighting in Afghanistan and Iraq and is not yet getting to grips with military spending, according to a top analyst in Washington.

A report by Anthony Cordesman of the Center for Strategic and International Studies blames the Obama administration for not making “realistic efforts” to estimate the future cost of operations in both countries. It warns that “the Afghan war is almost certain to put major new pressure on the defence budget in fiscal year 2012 and beyond”. Current US defence spending is more than $700bn a year.

While President Barack Obama promised last December to begin a transition to Afghan forces in July next year, the administration now says as few as a “couple of thousand” of the US’s 100,000 troops could leave Afghanistan then.

Officials such as General David Petraeus, the commander of the US and Nato forces, now emphasise a “thinning out” rather than an exit of US forces from specific provinces and shifting some troops from one part of the country to another. Meanwhile, building up Afghanistan’s police force and army is expected to cost tens of billions of dollars.

US forces are also still fighting in Iraq, despite Mr Obama’s announcement of the end of the combat mission in the country. The Pentagon announced a new fatality on Monday.

Mr Cordesman’s report also says that plans by Robert Gates, defence secretary, to find $100bn in savings over five years would generate only about half that figure even in the best-case scenario and will merely “buy time” until the 2012 budget request.

The report comes at a time when defence spending is under increasing scrutiny. Democratic legislators such as Barney Frank, the chairman of the House financial services committee, are calling for bigger cuts, a push resisted by conservative groups.

Mr Gates has sought to steer a middle way, pushing for a 1-2 per cent annual increase in defence spending over the medium term, but championing the proposed savings as a way of boosting efficiencies and getting resources to troops in the field.

Mr Cordesman argues that all spending is affected by the deficit and that “a potential crisis in entitlements spending …will begin to sharply accelerate in fiscal year 2014”.

But conservative groups such as the American Enterprise Institute and the Heritage Foundation stress that US defence spending is near historic lows.

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