COPENHAGEN — China and the United States were at an impasse on Monday at the United Nations climate change conference here over how compliance with any treaty could be monitored and verified.

China, which last month for the first time publicly announced a target for reducing the rate of growth of its greenhouse gas emissions, is refusing to accept any kind of international monitoring of its emissions levels, according to negotiators and observers here. The United States is insisting that without stringent verification of China’s actions, it cannot support any deal.

The stalemate came on a day of public and private brinkmanship as the talks moved into their second and final week. Earlier Monday, a group of poor nations staged a brief walkout from the bargaining table, and a chaotic registration system left thousands of attendees freezing outside the conference hall and forced the temporary closing of the subway stop near the Bella Center, where the meetings are being held.

The slow progress of the climate negotiations could pose problems later in the week, when the heads of government begin arriving. It is not customary for so many technical, financial and emotional issues to be unsettled when national leaders sit down to negotiate an agreement. President Obama and other world leaders have said that they hope to reach some interim agreement at the Copenhagen talks, but that a binding global accord is not likely to be completed until next year.

Negotiators for the United States and China have been trading public accusations in recent days and making little progress in negotiations on the critical issue of treaty compliance.

Chinese negotiators have said little during formal negotiation sessions here, where they have been working in partnership with the developing countries. They have made clear that they do not expect money from the industrial powers to help make the shift to a more energy-efficient economy.

But they will not accept any outside monitors to ensure that they are indeed making the changes that they have promised to reduce the amount of carbon dioxide and other pollutants emitted per unit of economic output.

“I think there’s no doubt that China, when it says 40 to 45 percent reduction in energy intensity, is serious about that,” said Ed Miliband, the British secretary of state for energy and climate change. “The more challenging hurdle is finding a formula for ensuring the outside world that an avoided ton of gas is in fact a ton.”

He Yafei, the Chinese vice foreign minister, said China’s laws would guarantee compliance.

“This is a matter of principle,” even if it scuttles the talks, he said in an interview with The Financial Times.

American officials said that despite nearly a year of negotiations with the Chinese, there were still fundamental problems that may not be fixed here before the meetings end. The United States says it believes that the Chinese emissions target is too low — a top American official called it “disappointing” the day it was announced. Without a stronger emissions commitment and an agreement to international monitoring by China, Congress is unlikely to approve a tough new domestic climate regime for the United States.

“If China or any other country wants to be a full partner in global climate efforts, that country must commit to transparency and review of their emissions-cutting regime,” said Representative Edward J. Markey, Democrat of Massachusetts and a co-sponsor of the climate and energy bill that passed the House in June. “Without that commitment, other governments and industries, including those in America, will be hesitant to engage with those countries when they try to partner on global warming.”

And the Chinese refusal to accept verification measures could also lead to calls for punitive tariffs on Chinese goods coming into the United States. The House bill allows for the imposition of tariffs on goods from countries that do not constrain their carbon output. A group of 10 Democratic senators wrote to Mr. Obama two weeks ago warning that the Senate would not ratify any treaty that did not protect American industry from foreign competitors who do not have to meet global warming emissions limits.

That threat could, paradoxically, help drive the Chinese to cement a deal here, an American official said. “Their No. 1 motivation is to avoid border tariffs,” the official said.

Barbara Finamore director of the China program for the Natural Resources Defense Council, said the top Chinese leadership was pursuing a cautious and calculated strategy as the talks near a decisive phase this week.

“They’re going to wait until the last hour of the last day and just as the other side is walking out they’ll say, ‘Hey, come back.’ Just as they do every day in every market in China,” Ms. Finamore said. “That’s why they’re the best negotiators in the world.”

As the dispute between China and the United States was playing out in private, a group of poor nations threw the talks off track for a time with a public protest. They complained that the industrial countries were doing too little to curb their own climate-altering emissions and consigning them to perpetual poverty.

Representatives of several African officials demanded that the rich countries sign a binding treaty that included a large transfer of wealth to the developing world. They brought the public sessions of the meeting to a halt at midday, but delegates began returning to the large conference hall as evening fell, and the talks resumed in desultory fashion.

John Hay, a spokesman for the United Nations body sponsoring the conference, said: “The plenary was suspended. A slew of technical meetings have not taken place. It’s an indication of how adamant the G-77 are about these issues,” he said, referring to the group of less-developed nations.

In New York on Monday, Ban Ki-moon, the United Nations secretary general, warned the negotiators in Copenhagen that leaving too much for the heads of state and government to hammer out at the end of the week risked enfeebling any final deal.

“There is no time left for posturing or blaming,” he said at a news conference, before leaving for the Danish capital. “If everything is left to leaders to resolve at the last minute, we risk having a weak deal or no deal at all, and this will be a failure of potentially catastrophic consequences.”

Todd Stern, the chief American negotiator, acknowledged that Monday had been a difficult day but said that progress continued to be made.

“In any big and complicated negotiation, and this may be the biggest and most complicated ever, it never goes smoothly,” he said. “It never goes as planned. There’s always bumps. There’s always zigs and zags, people getting up and down, and that’s to be expected.”