By Barbara Lewis

BRUSSELS (Reuters) - More than 50 top European and U.S. scientists have written to the European Commission president urging him to press ahead with a plan to label tar sands as more polluting than other forms of oil, in defiance of intensive lobbying from Canada.

The draft law was kept on ice during trade talks between the European Union and Canada, the world's biggest producer of oil from tar sands, which culminated in a multi-million-dollar pact signed earlier this year.

EU sources, speaking on condition of anonymity, have said political momentum behind even bigger trade talks between the United States and Europe could freeze the EU tar sands plan for good, as it would hobble billions of dollars' worth of transatlantic trade in oil products.

The 53 scientists who have written to President Jose Manuel Barroso include professors from Harvard, Stanford and Columbia in the United States, Aberdeen and Edinburgh in Scotland, University College in Ireland and Heidelberg in Germany.

They say the EU draft law, which would label fuels according to how much carbon they emit over their entire wells-to-wheels lifecycle, is scientifically sound, after criticism from the oil industry that it is not.

In the letter dated December 16, they say the policy would ensure investment in cleaner fuels and for the first time hold the oil industry accountable for carbon emitted during production of the fuels they sell in Europe.

"We live in an era during which it has become clear that we cannot burn all of the fossil fuels without causing dangerous climate change," the letter, seen by Reuters, said.

Peter Smith, a professor at the University of Aberdeen, said he signed the letter because fuels must be assessed "on the basis of the damage that they do".


EU member states approved legislation in 2009, with the aim of cutting greenhouse gases from transport fuel sold in Europe by 6 percent by 2020, but failed to agree how to implement it.

Named the Fuel Quality Directive (FQD), the law has been in limbo almost ever since. Oil companies, such as BP, and countries led by Canada have spoken out against it, saying it is unfair and unscientific.

To fend off the criticism, the European Commission said last year it was assessing the business impact of its proposal, but has yet to publish the results.

EU sources say they do not expect publication of the Commission's impact assessment until after a major chunk of environment and energy policy set to be announced in January.

In a statement, the Commission confirmed it had received the letter and would reply.

"The Commission has consulted widely on this complex file and is in the process of finalizing the impact assessment," it said.

(Editing by Andrew Roche and David Evans)