PARIS, May 15 (Reuters) - Failure to strike a global trade deal could have consequences beyond the world of commerce and make it harder to tackle climate change, the head of the World Trade Organisation (WTO) said on Tuesday.

"If there were to be a failure, it would be a serious blow to the multilateral ... system and in coming years we will need that system more," WTO Director General Pascal Lamy told a seminar on trade in Paris.

"I don't think it will be possible to deal on climate change issues, which are 10 times more complicated, if it is not through multilateral negotiation," he said.

The United States, Europe and some of the world's big developing economies remain divided on how best to tackle global warming, with many countries resisting emission cuts targets.

The WTO's 150 member countries are trying to overcome deep differences, mainly on farm trade, to save talks that were launched more than five years ago to boost the global economy and help fight poverty.

Lamy said the negotiations were now making progress again after a suspension last year, but not quickly enough. "The negotiation is not deadlocked any more. It's moving, maybe not at the speed we would all love it to, but it's moving," he said.

Trade ministers from around 20 countries gathered in Paris for discussions on Tuesday and Wednesday on how to move ahead with the negotiations. On Thursday and Friday, the United States, European Union, India and Brazil -- the core four members of the WTO -- are due to meet in Brussels.

The so-called G4 group is aiming for a full WTO deal by the end of this year, after which negotiations risk being sidelined by campaigning for the U.S. presidential election and several further years of delays, trade officials say.

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