Ministers from India, Brazil, Japan, the European Union and the United States were to attend the gathering on Monday in London, and wider meetings on Tuesday and Wednesday in Geneva, that could be crucial in deciding whether next month's meeting of ministers from all 148 WTO members in Hong Kong is a success.
Lingering disagreements have jeopardised the 13-18 December meeting, which aims to resolve many of the issues that have been blocking the Doha round of trade talks - named for the Qatari capital where it was launched in 2001.
"This is a critical week for these negotiations, there's no two ways about that," said Keith Rockwell, spokesman for WTO Director-General Pascal Lamy.
Lamy was to meet with the ministers on Monday afternoon.
Rockwell said he would listen to them and stress the urgency of the situation. Negotiators are far from producing a draft version of the Hong Kong declaration - and without that there is little hope of success by the end of the year.
Poor countries' lot
The meeting is being hosted by India. Commerce Minister Kamal Nath said he would be stressing the importance of improving the lot of poor countries, especially in agriculture.
"Agriculture for some countries is commerce, while for some countries, like India, agriculture is subsistence involving 650 million farmers," he said.
Rob Portman wants Europe to
cut agricultural tariffs
Negotiators are trying to agree on a binding treaty that aims to boost the global economy by lowering trade barriers across all sectors, paying particular attention to the concerns of developing nations. The round is already well behind an original December 2004 deadline.
Last week, the US trade ambassador, Rob Portman, urged European negotiators to promise deeper agricultural tariff cuts at this week's meeting. Portman, who was to attend the London talks, warned that the Hong Kong meeting could be jeopardised if the EU does not make the cuts.
The EU has offered to reduce agricultural tariffs - but not as much as other big agricultural producers are demanding, and it wants concessions in other areas, notably service industries and market access for industrial goods.
EU Trade Commissioner Peter Mandelson told the BBC on Monday that the talks "have been pushed into a sort of agricultural siding by some very aggressive agricultural producing countries whose interests do not necessarily coincide with the bulk of developing countries".
Asked about US insistence that the EU has not offered a large enough cut, Mandelson said: "The US would say that, wouldn't they?"
"Agriculture for some countries is commerce, while for some countries, like India, agriculture is subsistence involving 650 million farmers"
Indian Commerce Minister
He also insisted that he is moving forwards with the EU offer despite anger from France, which believes Mandelson has already given away too much.
France has previously threatened to veto any deal to liberalise world trade if Mandelson makes excessive concessions. Indian minister Nath said the EU offer was not yet good enough.
"We welcome the offer of the EU, it is a step forward. But it cannot be that you give an inch and ask for a mile," he said.
On Tuesday, the negotiators from the five countries will move to Geneva, where the WTO is based, to hold wider talks. Some 20 to 40 ministers from across the globe are expected to attend the talks over one or two days.