In an interview with Reuters, Mandelson deflected criticism at the weekend by French President Nicolas Sarkozy that the European Union was making too many concessions on farm trade, saying he did not feel his hands were tied in the talks.
"The constraint on me is what others amongst the emerging economies are prepared to do in industrial goods -- in non-agricultural market access," Mandelson said.
"If their apparently low level of ambition continues, it's going to make my position as Europe's negotiator quite hard."
He said he would do his utmost to prepare for a possible meeting of World Trade Organisation ministers in April.
The putative gathering is being billed as yet another last chance to make a breakthrough in the Doha round of market-opening talks, which was launched in the Qatari capital in 2001.
"But Europe needs greater engagement amongst its negotiating partners," said Mandelson, who was wrapping up three days of talks in Beijing.
He said he had been encouraged by the position China had taken on lowering barriers to trade in industrial goods and services as well as on trading rules. However, it remained defensive on agriculture.
"But unreasonable demands are not being made on them in that area, so I hope they will be more forthcoming in the other parts of the negotiation," he said.
"I wish they were showing a stronger lead and a clearer engagement over the world trade talks."
Sarkozy said on Saturday that he would oppose any WTO deal that went against the interests of France and the 27-nation EU, especially in agriculture.
Mandelson said Sarkozy was right to sound a note of caution about the need for a balanced outcome of the Doha round.
"I hope he will judge the talks in wider terms than agriculture alone," the trade chief said.
"But I welcome France's commitment to a successful outcome. He restated that, even though he chose to emphasise the conditions he was attaching to any deal."
Mandelson, who negotiates on behalf of the EU, said he had no complaint about the room for manoeuvre he had been given by member states.
"We've made good offers. Frankly, we are being more forthcoming than any of our negotiating partners," he said.