"The good news is that we all agree that export subsidies should be eliminated," US farm trade negotiator Allen Johnson said during yet another negotiating session.

"We all agree that this historic step has to be taken," he told journalists as the session drew to an end at WTO headquarters in Geneva on Friday, although he admitted the negotiators were still trying to figure out how.

Farm subsidies were at the heart of the collapse of a WTO ministerial meeting in Cancun, Mexico last September.

Poor countries rounded on the payments made to farmers in places like the European Union and the United States, warning that their own produce was unfairly priced out of world markets, while rich countries barely budged.

Agriculture has weighed on global trade liberalisation since the 1980s and was only resolved piecemeal in the "Uruguay Round" of trade talks which set up the WTO in 1995, with a promise of more to come.

Since then, the WTO member states have struggled to fulfil that promise, culminating with their spectacular deadlock in Cancun.

But two months ago, the EU offered to negotiate a date for the elimination of its export subsidies, although the politically-charged proposal upset France and several other EU members with large farming constituencies.

Brussels also said it was looking for "parallelism": in the jargon of the trade world, similar concessions from the United States on export credits or prices set by wheat boards in Australia and Canada.

That step appears to have stirred the talks on the critical "modalities" due by the end of July, which will effectively shape an eventual agriculture deal.

"There has been some movement for the first time on parallelism," a WTO official said on condition of anonymity after the latest meeting in Geneva.

Johnson said the member states had reached "a consensus" on the need to bring "disciplines" to all forms of export subsidies.

"Exactly how we do it is what we're talking about," he added.

The US negotiator also said there was "growing consensus" on the need to reduce other forms of agricultural subsidies paid to farmers, starting with the highest ones.

As for levering open markets to imports -- another key poor country demand -- Johnson also detected "convergence" among member states on the need to reduce the highest tariffs more, while allowing countries to protect some "sensitive" produce.

But time is running short. The 147 negotiators have another four weeks to relaunch the whole Doha round of trade talks, with only three more days devoted to agriculture on July 14 to 16.