The European Union has offered to cut its farm tariffs by 60% to kick-start trade talks in Geneva.
EU trade commissioner Peter Mandelson urged Brazil, India and China to reciprocate by slashing their industrial tariffs.
The US trade chief also vowed to help make the talks succeed if emerging nations made a contribution.
But developing countries warned that rich nations were expecting too much from their poorer counterparts.
Indonesia's trade minister, Mari Pangestu, said rich nations' hopes for an increased share of global trade should take a back seat to the development goals of the current trade round.
Brazil's foreign minister Celso Amorim said emerging economies, such as China, India and Brazil, were already offering substantial concessions and that developed countries should not expect too much.
Ministers from 35 nations are trying to reach a deal in talks at the Geneva-based World Trade Organization.
The Doha round of trade talks began in 2001. Discussions have so far foundered over the extent of cuts to farm subsidies and how far trade in services such as banking should be liberalised.
The EU previously offered to cut farm tariffs by 54%.