The US is seeking to extend its control over the day-to-day running of Afghanistan with the appointment of an international "high representative" in Kabul in an attempt to bypass Hamid Karzai's much-criticised government.

The initiative, being pushed by the US special envoy, Richard Holbrooke, has caused a split between Washington and its closest Nato allies, who believe it could further undermine the Afghan president's legitimacy and the United Nations' role in the country.

The proposal is part of a political strategy designed to accompany the dispatch of US reinforcements due to be announced tomorrow night by Barack Obama and ultimately provide an exit strategy.

The political package under discussion includes the installation of an Afghan chief executive at Karzai's shoulder in the government and closer international cooperation by a permanent "contact group".

The measures are designed to overcome the weakness and corruption of the Afghan government that the troops will be fighting to support. The British foreign secretary, David Miliband, has said the government would fall within weeks if Nato pulled out now.

Some European officials, including senior British figures, argue that the gains in efficiency achieved by appointing an international envoy with vice regal authority would be outweighed by the Kabul government's further loss of legitimacy.

"This has to be Afghan-owned or it's not going to work," a top European official said. European states and Canada have a more positive view of the UN's performance than the US.

Following his re-election in fraud-ridden elections, Karzai has promised his Nato backers he will a take a tougher line against corruption and has made greater efforts in supplying recruits for the Afghan army and police force whose training and deployment represent the core the exit strategy to be outlined by Obama.

Western governments are sceptical about whether Karzai will be able to reform as quickly as they would like to enable them to withdraw troops, and they are beginning to discuss contingency plans to improve Afghan governance by bypassing the president if necessary.

Foreign ministers from the countries with most troops involved – the US, Britain, Germany, France and Canada – discussed the next steps at Karzai's inauguration on 19 November.

Holbrooke pursued the issue in visits to Berlin and Paris, and in conversations with British officials last month. Final decisions will be taken at the London conference on Afghanistan in late January.

Holbrooke in particular believes the UN mission is ineffectual and soft on the Afghan government's alarming record of corruption. He is pushing for the appointment of a high representative for the international community, modelled in part on the post of the same name in Bosnia.

He has met resistance from European states and Canada that have more faith in the Norwegian head of the UN mission, Kai Eide.

"This is something Holbrooke is pushing but it's not set in stone yet," said a senior defence official from a country with troops on the ground. "It is a way of getting around Kai Eide but some of the allies have a lot of time for Kai. He has achieved a lot. He persuaded Karzai to hire some of his better ministers. He just goes about it in a quiet way."

A European diplomat portrayed the initiative as an attempt to restore US influence at the heart of the international co-ordination effort after Peter Galbraith, an American diplomat, was forced out of his job as the second-in-command at the UN mission in September because of a personality and policy clash with Eide.

"In a way, the idea of this is to replace Galbraith, " the diplomat said.

The Holbrooke-led campaign against Eide drew support last week from the International Crisis Group. In a report on Afghanistan's "crisis of governance" on Wednesday, the independent organisation recommended Eide's resignation "since he has lost the confidence of many on his staff and the necessary trust of many parts of the Afghan polity".

Eide's term ends in March and some European countries have suggested he could be replaced then by a "super-envoy", perhaps combining the UN post with a Nato civilian role.

The former Lib Dem leader Paddy Ashdown was initially approached for such a job in early 2008 but his appointment was blocked by Karzai. The appointment of Ashdown or another leading British figure in such a powerful role is still seen in Kabul and some capitals as problematic because of Britain's imperial history.

Another name mentioned as a possible international high representative is the current US ambassador in Kabul, Karl Eikenberry, but he has recently clashed with the American Nato commander in Afghanistan, General Stanley McChrystal, over whether Washington should send more troops.

Nick Horne, a former UN official in Afghanistan who resigned at the end of October over the failure to achieve political reform, said the new international representative "would have to be someone of international stature".

"He has to have the full support of the international community, and the confidence of the Afghan people", Horne said.