Next week, President Barack Obama and Chinese President Xi Jinping will add to earlier pledges to cut greenhouse-gas emissions with specific guidance on what the two countries will do at home to keep climate change at bay, officials said.

The United States and China announced Tuesday that cities, states and provinces in both countries would commit to taking parallel steps to address climate change.

The participating Chinese cities and provinces, which represent about 25% of total urban emissions in that country, will offer plans to have their emissions peak sooner than the national target of 2030.

Beijing and Guangzhou, two of China’s largest cities, will aim for their peak emissions to come as early as 2020.

Climate officials and leaders from both countries are meeting in Los Angeles this week to lay out the steps the regions will take and to set the groundwork for next week’s summit between the two presidents.

U.S. officials said the Obama-Xi summit is part of an effort by the two biggest polluters—which account for more than a third of global greenhouse-gas emissions—to demonstrate progress on meeting the terms of a bilateral accord reached in November.

White House press secretary Josh Earnest said Tuesday that Mr. Obama would use next week’s meeting to discuss additional opportunities for U.S.-China cooperation on cutting carbon pollution.

The U.S. commitments are coming from states such as California and Connecticut and an array of cities including Atlanta, Boston, Los Angeles, Washington, Seattle, and Houston.

The U.S. pledged last year to reduce carbon-dioxide emissions by between 26% and 28% by 2025, compared with 2005 levels, while China said it would make sure its emissions peak by 2030 or earlier.

To achieve its goal, the Obama administration this summer finalized new rules for coal power plants.

Some prominent Republicans in Congress say the moves will damage the U.S. economy and are moving to block the rules in court; they are seeking to undermine Mr. Obama’s authority to conclude a binding agreement among nearly 200 nations, which is meant to come to a head in Paris later this year.

“Last year was a year for setting goals and targets,” said Brian Deese,a senior White House adviser who specializes in climate issues. “This year needs to be a year of implementation.”

The Chinese cities’ commitment to early peaking highlights the country’s efforts to achieve its national target as early as possible, Mr. Deese said, and the joint U.S.-China actions show the seriousness of the effort to meet the terms of the countries’ agreement.

The cities, states and provinces that sign the declaration and pledge to address climate change also will track and report their emissions on a regular basis. Such commitments create a measure of accountability, Mr. Deese said.

For the world’s highly developed economies, a top goal of the agreement expected in Paris in December is signing up fast-growing emerging markets, which have avoided the burden of reducing emissions in previous agreements organized by the United Nations.

The U.S.-China climate discussions will spill into a range of wider discussions among countries gathering later this month at the U.N.

China’s move last year reassured environmentalists about Beijing’s commitment, but India and other emerging markets haven’t submitted their own proposals for cutting emissions through the Paris accord.

Republicans in Congress say China got off easy by agreeing to start reducing emissions only in 2030. A slowing Chinese economy and rebalancing away from heavy manufacturing could allow China to achieve the goal much earlier without significant costs, according to some climate experts.

A survey this summer by the China Carbon Forum, an independent organization that promotes efforts to curb climate change in China, found that 82% of industry experts say China will reach its emissions peak before 2030, with 39% saying before 2025 and 16% before 2020.

Mr. Earnest, the White House press secretary, said the pledges announced Tuesday signaled that China’s emissions could peak before 2030.

Environmentalists have cheered China’s commitment to boosting green energy, a shared goal U.S. officials say will likely come up during Mr. Xi’s visit.

The two leaders may also tackle some of the thorny unresolved issues of the international climate talks, including poorer countries’ insistence that developed economies help finance their transitions at a cost of around $100 billion a year for all countries combined.

“Anything that signaled a preparedness to find some common ground on the outstanding issues would be welcomed,” said Jo Tyndall, New Zealand’s climate-change ambassador, in Washington last week.