Republicans on Thursday accused John Kerry, President Biden’s special envoy for climate, of being soft on China as he prepared to travel to Beijing to restart discussions between the world’s top two polluting countries.

In a contentious hearing before a House Committee on Foreign Affairs panel, Republicans attacked Mr. Kerry for not doing enough to persuade China to cut its greenhouse gas emissions. At the same time, several also sought to portray Mr. Kerry as putting Chinese interests above those of the United States by negotiating with America’s top economic rival.

Mr. Kerry expects to arrive in China on Sunday for three days of climate talks. He told lawmakers that he believes the Chinese government must reverse its growing use of coal-fired power plants, which has helped to make it the world’s biggest polluter. But he also made a point of praising China for deploying more wind, solar and other renewable energy than the rest of the world combined.

Mr. Kerry said it was important to try to find a way that would allow China and the United States to work together to reduce global emissions, despite the tensions between the countries over trade, human rights and other issues.

“China is the world’s largest economy, and the world’s largest emitter,” Mr. Kerry said, insisting it would be “malpractice of the highest order, diplomatic and political,” for the United States not to hold talks with China.

The hearing underscored the tightrope Mr. Kerry walks in seeking cooperation with Beijing while Republicans and some Democrats try to outdo each other with tough rhetoric on China. It also exposed how little leverage the United States has to pressure the Chinese government to act faster to cut its carbon emissions.

“What is the U.S. doing to force China to reduce its emissions?” asked Representative Nathaniel Moran, Republican of Texas.

Objecting to the use of the word “force,” Mr. Kerry did not directly address what, if anything, the United States could do to compel China to change course, but he said that dialogue was what was really needed between the two countries.

He also noted that lawmakers are considering a plan similar to one in Europe that would tax iron, steel and other imports that are made by countries without strong climate laws, like China. “That is gaining some steam legislatively because I think people are frustrated with what’s happening,” he said.

Republicans said they were skeptical that Mr. Kerry would succeed given that China has been investing in new coal-fired power plants, despite its acknowledgment that global emissions must come down.

“We have not seen any real deliberate effort on their part to match the United States’ efforts,” Mr. Moran said.

Scientists say if China’s emissions continue to rise, by midcentury it would overtake the United States as the country that has pumped the most greenhouse gases into the atmosphere since the start of the Industrial Age. All that pollution from industrialization has helped to warm the planet an average of 1.2 degrees Celsius.

Scientists say 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, is the threshold beyond which the impacts of climate change — drought, heat, wildfires, floods — will outpace humanity’s ability to adapt.

Another issue raised at the hearing was China’s classification within the United Nations climate body as a developing country. As such, it has decided to cut its emissions at a slower pace than the United States and the European nations. China has also argued that it should not face the same financial obligations to help poor nations cope with climate impacts.

China has said its emissions will continue to grow until 2030, when it will start reductions. It said it would stop adding carbon pollution to the atmosphere by 2060. President Biden has promised the United States will cut its emissions in half from 2005 levels by the end of this decade and stop adding carbon by 2050.

“How in the world can the second-largest economy maintain to you and the rest of the world, with a straight face, that they are a developing nation, giving them preferential treatment?” asked Representative Michael McCaul of Texas.

Mr. Kerry said that he agreed with Republicans who said China should be treated as a developed nation and that the matter would be revisited next year.

The hearing also featured a series of testy personal attacks.

Representative Brian Mast, Republican of Florida, told Mr. Kerry he was “not representing the United States of America” but rather a “far-left radical agenda.”

Representative Cory Mills, also a Florida Republican, sarcastically thanked Mr. Kerry for taking the time to fly in on his “private jet.”

Mr. Kerry called Mr. Mills’s comment “pretty stupid” and said he does not own a private jet but flies commercial.

Representative Scott Perry, Republican of Pennsylvania, showed charts he claimed proved the world is not warming. That prompted Mr. Kerry to call the lawmaker’s views, which run counter to the conclusion of scientists around the globe, “shocking.”

Mr. Perry retorted, “They’re grifters, like you are, sir,” eliciting gasps from both sides of the aisle.