The Obama administration is hoping for fresh momentum toward a climate treaty during international talks this week in Lima, Peru, but the immediate challenge may be to simply keep the negotiations from breaking down.

Officials from 190 countries gathered in the Peruvian capital on Monday for 12 days of meetings intended to lay the foundations for a carbon-cutting pact that would be signed a year from now in Paris. But achieving even modest progress will require overcoming stark differences over what the accord should look like and who should pay for it, diplomats acknowledged as the talks got underway.

On an opening day infused with ceremony and symbolism - including the unfurling of a protest banner by the environmental group Greenpeace on a hill overlooking the famous Machu Picchu ruins - U.S. officials expressed guarded optimism, saying prospects for a climate deal have brightened substantially following last month's U.S.-China agreement on cutting greenhouse gas emissions.

But the officials acknowledged that old disputes over money and fairness carried the potential for sabotaging the negotiations, as they have during previous attempts to forge a deal.

"There is an opportunity here - probably more of an opportunity than there has been for a very long time," said Todd Stern, the State Department official who will lead the U.S. negotiating team in Lima. "But that opportunity is going to be contingent on countries acting with a degree of balance and pragmatism that can allow this agreement to get done."

The U.N.-sponsored talks in Lima are intended to resolve technical and financial issues in advance of final negotiations for a treaty that would be signed in Paris next December. A successful effort, diplomats say, will put the world's nations on a path toward rapidly reducing emissions of carbon dioxide and other gases that scientists say are contributing to a dangerous warming of the planet.