The growing trade row between the US and China could threaten the facade of unity that G20 leaders are hoping to maintain at the Pittsburgh summit.
Brazilian cars being loaded for export in Rio de Janeiro Brazil fears a trade deal could have a big impact on its car industry
The US decision to slap punitive tariffs on Chinese tyre imports - at the urging of US trade unions - has given a strong signal that the Obama administration is not prepared to put free trade at the top of its political agenda.
This will worry countries like Britan and Japan who fear that a retreat to protectionism, as in the 1930s, could hamper the world economic recovery.
But the US also has a hidden agenda in its aggressive trade move - its aim is to force China to open its own domestic markets further.
President Obama has accepted the advice of his economics team that the US cannot borrow itself out the recession this time, so it must export its way out. And opening up the Chinese market to US goods is essential to that strategy.
Protectionist fears
It is not just the US-China spat that is worrying observers.
With the world in the grip of a recession many countries are now turning to bilateral trade deals and protectionism in an effort to ensure the future of their national industries and preserve access to key markets.
And with the so-called Doha round of talks - aimed at liberalising trade in agriculture and services and helping developing countries - currently stalled after collapsing last year, many hold out little hope of a breakthrough on the issue.
Despite a marathon round of pre-Pittsburgh talks and meetings the new US trade representative, Ron Kirk, has failed to make any headway with the leading voices from the developing world - India and Brazil.
Impasse
A disagreement between India and the US sparked the collapse of trade talks in Geneva last year.
At the heart of the disagreement between the US and developing countries has been the reluctance of those countries to fully open their own markets to food imports from the West - and especially the US.
India fears its smaller-scale farmers will be unable to compete with the sophisticated US agricultural machine. These fears were heightened last year, when the cost of food soared worldwide, and in the Indian general election in the spring both parties said they would protect small farmers.
However, on the other side of the fence, the US and Europe say that if they are going to open their markets fully to agricultural products from developing countries, it is only fair that developing countries do the same.
The main beneficiary of any agricultural liberalisation would be the bigger developing countries - Brazil, Argentina and South Africa - with very large and efficient agricultural sectors.
However, they object to demands from the US and Europe that they fully open up their manufacturing sectors to Western imports as part of any trade deal.
Brazil, which has built up a huge car manufacturing business behind trade barriers, is reluctant to take such steps, especially during a recession from which they have been largely immune.
US politics
Indians protest against trade deal Indian farmers have shown widespread opposition to opening up trade barriers
The biggest obstacle to any trade deal, however, remains the attitude of the US Congress, which is now controlled by Democrats.
With rapidly rising unemployment in the US, many Democrats are extremely sceptical of any trade deals, especially those which do not also include a provision about ensuring labour rights in developing countries - something the developing countries are dead set against.
In order to pass a trade deal, the Obama administration would need to get fresh negotiating authority from Congress, something that would require strong political will.
But with the administration embroiled in the fight over health care reform and climate change legislation, this is unlikely to emerge any time soon.
Protectionist pressures
Indeed, many countries, including the UK, are worried by the growing protectionist pressures in the US - especially in relation to the $787bn fiscal stimulus package, which included a Buy American provision.
While there has not been a repeat of the experience of the 1930s, when countries raised trade barriers around the world thus making the depression worse, there are worrying signs that the US is not alone in its actions.
US trade representative Ron Kirk So far potential trade partners have been unmoved by America's overtures
The World Trade Organisation has tracked more than 70 protectionist measures introduced by G20 countries since the crisis.
One of the most worrying is the increasing restriction on where financial institutions bailed out by governments can lend, which has been restricting capital flows to hard-hit developing countries.
It was notable that at the latest G20 finance ministers meeting, US Treasury Secretary Tim Geithner emphasized that the world had avoided falling into protectionism, while UK Chancellor Alistair Darling warned that this was still a significant danger.
As the crisis eases, the big exporting countries such as China and Germany are recovering the quickest.
Any serious revival of protectionism could put a stop to that, and therefore to the world-wide economic recovery as a whole.
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