Officials from nearly 200 countries working to negotiate a climate-change agreement are wrestling with the most basic question: whether key sections of the final pact should be legally binding. The European Union made it clear from the start of talks here that the climate deal set for completion next year should be airtight under international law, with legal consequences if countries stray from their commitments. “The European Union favors an agreement with binding greenhouse-gas reduction targets for all countries,” said Miguel Arias Cañete, the EU’s energy and climate commissioner. “We are yet to be convinced that an alternative approach will go for the same level of predictability.” But the U.S., the other giant economy active in the negotiations, is backing a hybrid approach developed by New Zealand. Under that plan, countries would be required to have an emission-cutting plan that would be enforced through domestic laws but not be binding under international law.