"We know that the president of the United States has asked for an extension of this," he said. "We know by experience there might be some discrepancy in the process and the TPA might lapse, although negotiations would continue."

Fast track, formally known as trade promotion authority, or TPA, allows the White House to negotiate trade deals that Congress must approve or reject without making any changes. It expires at the end of June, and the Democrat-controlled Congress might not renew it.

Many consider fasttrack vital to the success of the Doha round of world trade talks.

Speaking in Mexico City, Lamy also said the United States needed to make a new offer on reducing trade-distorting agriculture subsidies if the Doha talks were to progress.

"We need new numbers from the US on what they are ready to do to reduce their trade distorting agricultural subsidies," Lamy said.

On a recent trip to Latin America, US President George W. Bush said Washington was prepared to reduce farm subsidies but wanted to ensure market access for its goods.

The WTO launched its Doha round in 2001 to cut barriers to trade around the world as a way to lift millions of people out of poverty and boost the global economy.

Trading powers have been locked in behindthescenes efforts in recent weeks to galvanize the negotiations, which were relaunched in January after a six-month suspension.

Other nations of the 150-state WTO are growing restless as the so-called G4 — the EU, the United States, Brazil and India — seek common ground in bilateral meetings.

Lamy said those talks are at an "absolutely crucial" point as time runs out on the TPA. He said the TPA makes the negotiation process easier, though it is not required for talks to continue.

Meanwhile, a new study said most developing countries stand to gain from successful completion of the World Trade Organization’s protracted Doha negotiations, but a few would likely lose exportmarket advantages, according to a new study.

Developing countries that now have preferential access to the US or European markets would have less product access in these markets under various potential versions of a WTO Doha agreement on multilateral trade liberalization, according to a working paper released this week by the National Bureau of Economic Research.

"Whether a country loses market access following trade liberalization critically depends on how much of its exports currently benefit from existing preferences," according to the study by New York Federal Reserve economist Mary Amiti and University of Chicago economist John Romalis. The two wrote the paper while working for the International Monetary Fund.

Mexico, countries in sub-Saharan Africa and some Caribbean countries are among the minority that would likely see net loss of market access in the US or Europe if the WTO talks succeed, the authors found.

Sub-Saharan Africa could lose US demand because of current tariff preferences for its exports of oil and other minerals. Mexico could give up some relative advantage from the North American Free Trade Agreement. Haiti could lose demand for its clothing exports, while Dominca and St. Lucia could lose European demand for their bananas.