The Group of Eight (G8) summit in Germany is critical for the outcome of the World Trade Organisation's Doha round of negotiations on a global free trade deal, he said.
"The political stakes are very high. This seems to be leading negotiators, as we approach the deciding moment, to harden their positions rather than offering compromise and flexibility," he told members of the European Parliament.
"I believe we need the personal and active engagement of leaders of major economies to authorise the compromises to be made on all sides that can deliver a deal that is balanced, ambitious and fair."
The G8 summit was be attended by the leaders of key players in the Doha round -- the United States, European Union, Brazil and India.
Mandelson said he regretted signs from Brazil that it was prepared to "lower its ambition" for the negotiations. Brazil has said the United States and EU have not offered big enough cuts in farm protection to justify big cuts in tariffs on imports of industrial goods by developing countries.
"If others are going to lower their ambition, there is an obvious implication for the EU as well," he said.
Mandelson and his counterparts from the United States, Brazil and India are due to meet for five days from June 19, also in Germany, in what could be a last-gasp bid for a breakthrough in the global trade talks.
Any deal would also have to be backed by the WTO's full 150-country membership. Negotiators are in a rush because next year's US presidential election and other factors could push the Doha round back by several years.
It was launched more than five years ago in a bid to steady the global economy after the 2001 attacks on the United States, and to help developing countries trade their way out of poverty.
The round has been mired in arguments about how to bring down barriers to commerce, mainly in farm and industrial goods. (Reuters)
