LE BOURGET, France — U.S. officials labored on two fronts Tuesday to secure an international agreement on climate change, haggling with diplomats over the scope and costs of a proposed accord while fending off fresh attacks from Republican lawmakers who have vowed to torpedo any deal that emerges from the talks.

Secretary of State John F. Kerry, in France to lead the U.S. delegation, described broad momentum toward an accord but also warned of “sharp” differences that would have to be overcome if a deal is to be reached before the talks’ scheduled conclusion on Friday.

“A consensus is slowly being built,” Kerry told reporters after a day of private meetings at the Le Bourget conference center in Paris’ northern outskirts. But he also warned that the Obama administration would not accede to demands that Western nations accept financial responsibility for decades of greenhouse emissions that have caused the Earth’s atmosphere to warm.

“If you create a concept of liability you’ll have 100-to-nothing in Senate and 435-to-nothing in the House,” said Kerry referring to likely bipartisan opposition in Congress to a deal that puts the United States on the hook for economic reparations for  climate change. “If we’re going to have an agreement, let’s be smart about what we’re doing. And that’s what we’re trying to do.”

On Wednesday, diplomats from 195 countries attending the talks are expected to produce a new draft of the proposed climate accord that narrows differences over the key issues of transparency and compensation and financial aid for poorer countries. A bloc of developing nations that includes India is demanding that wealthier states finance their transition to cleaner energy while also compensating them for economic losses resulting from man-made climate change.

The leader of India’s delegation to the talks suggested Tuesday that the United States and other developed countries were morally obligated to pay for a problem that was largely created by the industrial West.

“We remain disappointed with the low level of climate ambition and support provided by developed countries,” said India’s environment chief Prakash Javadekar, who was joined at a news conference by officials from Brazil, South Africa and China, a bloc that, with India, is collectively known as BASIC.

But as diplomats huddled in private to try to close the gaps, a Senate committee led by GOP presidential contender Sen. Ted Cruz (R-Tex.) convened a hearing in Washington to question the scientific consensus that human activity is responsible for climate change. Cruz dubbed the hearing “Data or Dogma,” and called as witnesses several scientists who are skeptical of mainstream views on climate change.

“For 18 years there has been no significant warming,” Cruz said.

Kerry dismissed the hearing as a meaningless stunt. “One professor or scientist does not negate peer-reviewed studies by thousands of others over many years,” he said.

Another contentious issue at the Paris talks is how ambitious the accord should be in restraining the growth of greenhouse gases. U.S. and European officials have set a goal of limiting the rise in the Earth’s average temperature to 2 degrees Celsius over preindustrial averages. But some countries that face higher risks from climate change say the rise in temperatures should be capped at 1.5 degrees C. Scientists say neither goal is likely to be achieved unless the world’s nations commit to substantially higher reductions in greenhouse gas pollution.

Kerry said Tuesday that he would support a 1.5-degree target as an aspirational goal, one that countries may seek to achieve in the future as technology improves. “You can write that aspiration into the agreement in way that doesn’t make it the target guidepost,” he said.

More voices at the U.N. climate change conference have been calling in recent days for seeking to keep global warming below 1.5 degrees C,  even as some experts are questioning the extent to which it’s even possible. The world is already at about 1 degrees Celsius of warming, with about 400 parts per million of carbon dioxide in the atmosphere and concentrations growing by around two parts per million per year on average. Recent research suggests that to limit global warming to 1.5 degrees C, concentrations couldn’t exceed about 420 to 440 parts per million by 2100.