HONG KONG — Under pressure to reduce smog and greenhouse gas emissions, the Chinese government is considering a mandatory cap on coal use, the main source of carbon pollution from fossil fuels. But it would be an adjustable ceiling that would allow coal consumption to grow for years, and policy makers are at odds on how long the nation’s emissions will rise.

Senior officials are debating these issues as they formulate a new five-year development plan, to be finalized by the end of next year. China emits more carbon dioxide than any other country, so what President Xi Jinping and his colleagues decide will have far-reaching consequences for efforts to contain climate change.

China’s leaders have not detailed their views on coal or carbon emission limits. But there is robust support among senior policy advisers for a firm national cap on coal starting in 2016, Wang Yi, a professor at the Chinese Academy of Sciences in Beijing who studies environmental policy, said in a telephone interview.

“I think there’s a broad consensus on this, and it’s a question of how to implement it,” said Professor Wang, who is a senior member of China’s legislature, the National People’s Congress. “If we can have a cap on coal, that would almost be equivalent to a cap on carbon, because coal is such a dominant source of pollution and emissions.”