The major players at the World Trade Organisation are not any making grandiose claims for what the meeting Friday and Saturday can achieve.

But all sides know that something has to give if the WTO is to achieve its goal of establishing the broad outlines of a global trade deal by the target date of April 30.

WTO chief Pascal Lamy was to join the talks hosted by Brazilian Foreign Minister Celso Amorim along with European Union Trade Commissioner Peter Mandelson and US Trade Representative Rob Portman.

Mandelson said in Buenos Aires Wednesday that the meeting, at a hotel overlooking the sun-and-sand delights of Copacabana beach, was not aimed at clinching any breakthroughs.

Rather, he said, the meeting "will be an opportunity to understand the differences that exist among the key players to see how we could narrow the gap between us".

The 149 WTO members have already missed a series of deadlines to wrap up their "Doha Round" of negotiations launched in the Qatari capital in 2001.

A full ministerial meeting in Hong Kong at the end of last year produced only a loose framework for an accord and a new commitment to forge the main outlines by the end of April.

A follow-up gathering of six of the biggest players in London in mid-March explored new data showing the potential gains from ambitious tariff cuts, but made scant progress otherwise.

Developing countries led by big emerging markets such as Brazil and India insist the rich world, notably the European Union, must move first by dismantling generous agricultural subsidies.

The European Union, backed to an extent by the United States, retorts that developing nations must in return grant much greater access to its industrial exports and service industries.

The overall aim is to achieve a comprehensive agreement by the end of this year.

That is one deadline that really cannot be missed, given that in the middle of next year, the US Congress will regain the right to pick apart any trade accord negotiated by the administration.

In Rio this weekend, Portman hopes the parties "can build on their talks from London and move closer to establishing a framework in advance of the upcoming (April) deadline," the US trade chief's spokeswoman told AFP.