By Michael Wines

Nancy Pelosi, the House speaker, met China's two top leaders on Wednesday to discuss cooperation on energy and environmental problems, and Prime Minister Wen Jiabao said Beijing would join Washington to ''push for positive results'' at the next global warming summit meeting this fall in Copenhagen.

Mr. Wen's public statements, reported by the state's Xinhua news agency, offered no specifics, however, and some experts here noted that the two nations' official positions on reducing climate-changing pollution remained far apart.

Ms. Pelosi and five House legislators involved in energy and environmental issues met with Mr. Wen and separately with President Hu Jintao on the third day of an eight-day tour of China.

In a statement issued late Wednesday, a Pelosi spokesman said the meetings had also addressed North Korea's recent nuclear test and missile launchings, human rights issues, the global economic crisis and intellectual property rights. Beyond expressing general hopes that North Korea would resume multilateral talks and concern about China's human rights record, the statement offered little detail.

In a speech on Tuesday in Beijing, Ms. Pelosi, a California Democrat, called the climate change issue ''a game changer in the U.S.-China relationship'' and ''an opportunity we cannot miss.''

''We are the biggest greenhouse gas emitters in the world,'' she said, at a meeting of the U.S.-China Clean Energy Forum, an alliance of Chinese economic officials and American leaders from business and government. ''We have a responsibility to ourselves, to each other and to the world. We must work together.''

After Wednesday's meeting with Ms. Pelosi, Mr. Wen appeared to agree. ''China will cement policy dialogue with the United States, take the joint tackling of climate change as an important aspect of cooperation, and push for positive results in the Copenhagen climate change conference,'' the successor to the 1997 meeting in Kyoto, Japan, which produced the last global warming agreement.

Much of the world is looking to the United States and China, which together emit nearly half the world's climate-changing gases, to find common ground on a new treaty that will reduce pollutants.

The United States has said that any new global climate agreement will have to restrict the growth of emissions in China, the world's largest producer of greenhouse gases.

Just last week, however, China issued a new position paper on climate change that rejected any mandatory caps on its emissions and demanded that wealthy countries provide at least .5 percent to 1 percent of their gross domestic product to help developing countries upgrade technology and cope with the results of climate change.

A bill being considered by the House would compel the United States to reduce greenhouse gas emissions to at least 17 percent below 2005 levels by 2020, and to 83 percent below by 2050. But that plan is well below the opening demand by Chinese leaders, who want developed nations to reduce 2020 emissions by 40 percent from 1995 levels, and it falls short of commitments by the European Union as well.

American officials have already rejected the Chinese proposal as unattainable. The Center for American Progress, a Democratic-leaning research organization, said in a report published Wednesday that the House legislation was unlikely to win enough Chinese support for the two nations to present a united front at the Copenhagen talks in December.

A leading Beijing expert on climate change economics, Zhang Shiqiu, said Wednesday that she was optimistic that the two nations would reach some accord on global warming before the Copenhagen meeting. But she also cautioned that American negotiators needed to appreciate the steps that China had already taken to improve its environment.

''Many Chinese -- not only politicians, but academic society and the general public -- would say that before the U.S. blames China, the U.S. should clean up first,'' said Ms. Zhang, a professor of environmental economics and policy at Peking University.

By some estimates, China's huge package of stimulus spending aimed at addressing the global economic crisis includes more measures aimed at improving energy efficiency than the American package. The economic downturn has also reduced energy use, though most likely temporarily.

But China remains highly inefficient in energy use by global standards. And its rapidly expanding industrial economy, with its dependence on electricity from coal-fired power plants, is by far the world's fastest-growing source of carbon dioxide emissions.