Condoleezza Rice, the US Secretary of State, flies in to London today for crisis talks on spreading the burden of combat in Afghanistan, as Washington announced record defence spending.

The Pentagon submitted a new running budget of more than $515 billion (£260 billion) yesterday — the highest since the end of the Second World War. Defence chiefs have asked for an additional $70 billion to supplement the wars in Iraq and Afghanistan alone.

The record defence budget, contrasting sharply with the squeeze on domestic programmes such as health and education, threatens to reignite the national debate about the war, which has been pushed to the back of voters' minds by more pressing concerns about the failing economy.

Dr Rice will have to calm a growing row within Nato, fuelled by Robert Gates, the US Defence Secretary, over individual states' troop contributions to Afghanistan. New reports caution that Afghanistan risks collapse if the international community does not redouble its efforts there.

The Bush Administration is sending another 3,200 Marines to southern Afghanistan from March to September, and is looking to Britain to help to convince Nato allies to put together an equivalent European force to take over from it. Canada has threatened to pull out its 2,500 troops unless other countries share its combat burden in the south.

Nato defence ministers will meet in Vilnius, the Lithuanian capital, this week to try to find 7,500 more troops to reinforce the 42,000-strong force already deployed across Afghanistan. Mr Gates has written to all his Nato counterparts, including an unusually “direct and stern” missive to Germany, demanding that the country does its share. The letters have caused anger in Berlin and among other Nato allies, who believe that they are being dragged into American domestic politics during an election year.

Mr Gates has done himself few favours with his recent comments that some Nato forces did not know how to do counter-insurgency operations. The Nato operation in Afghanistan never foresaw the level of combat that it now faces.

Germany, among other Nato states, has strict caveats on the foreign deployment of its troops, dating back to the Second World War, which Washington is to lift.

With no such restrictions, Britain, the US, Canada, the Netherlands and Denmark have been burdened with the bulk of the combat in the south of the country, where the Taleban are concentrated.

Britain, still smarting from President Karzai's criticisms of its 7,800 troops in southern Afghanistan and the blocking of Lord Ashdown of Norton-sub-Hamdon as a United Nations super envoy, has so far steered clear of the public spat.

Washington and London, however, remain far apart on key policies in Afghanistan, mostly notably the issue of drug eradication on which the US believes that Britain has failed. Dr Rice will be pushing David Miliband, the Foreign Secretary, to accept Washington's plan for an Afghan National Army ground eradication force in Helmand, where most British troops are based. Washington blames British failures to stop record poppy production in Helmand for funding and fuelling the insurgency.

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