BRUSSELS, May 6 (Reuters) - Europe's trade chief appealed on Tuesday for urgent progress in long-delayed negotiations for a world trade deal, saying the next key step needs to take place by the end of next week.

"If people ask me now or later, I say there may not be a later for this deal. It's got to be now," European Trade Commissioner Peter Mandelson told reporters.

He called on other countries to set aside differences on trade in tropical farm products to allow a new set of compromises on the core farming and industrial parts of a World Trade Organisation deal to be proposed by WTO mediators.

"I would like to see texts appearing no later than mid-May, and that means no later than the end of next week," he said.

The WTO's Doha negotiations for a global trade deal were launched in 2001 to help poor countries export more and to boost the global economy. But they have missed a string of deadlines due to deep differences over how to lower barriers to exports.

Without a deal soon, the changeover of administrations in Washington and Brussels in 2009 risk causing several more years of delay, adding to concerns that support for free trade is giving way to protectionism as economic growth slows.

Talks have intensified in recent weeks but there has not been enough progress for the WTO to summon ministers to Geneva for a push for the long-elusive breakthrough in the round.

Mandelson said on Tuesday that he still hoped the ministerial meeting could take place in May or in June. Some officials say a meeting in July is more likely.

Mandelson said a breakthrough in May or June would still leave enough time for U.S. President George W. Bush to sign a final deal although the winner of November's presidential elections might need to "dot the i's and cross the t's."

The prospect of a new U.S. president getting involved in the Doha round worries some countries, especially after the Democratic rivals questioned the merits of new trade deals.

Some EU leaders, led by French President Nicolas Sarkozy, have also expressed concern that a Doha deal might be bad for Europe and there should be no rush to get one done this year.

Mandelson also urged members of South America's Mercosur bloc to step up progress this year on a long-stalled trade agreement with the EU.

"Obviously 2009 is not going to be a good year for multilateral trade discussions so we've got to increase efforts and achieve a successful conclusion to the negotiations this year," he told Latin American reporters in a teleconference from Brussels.

The EU's trade talks with Mercosur, which groups Brazil, Argentina, Uruguay and Paraguay, started in 1999 and have taken a backseat to the Doha round.