By Roberta Rampton and David Ljunggren

WASHINGTON/OTTAWA (Reuters) - U.S. President Barack Obama, Canadian Prime Minister Justin Trudeau and Mexican President Enrique Pena Nieto will commit to a new regional clean power goal at a summit this week in Ottawa, the White House said on Monday.

The leaders, meeting in Ottawa on Wednesday at the so-called "Three Amigos" summit, will pledge to have their countries produce 50 percent of their power by 2025 from hydropower, wind, solar and nuclear plants, carbon capture and storage, as well as from energy efficiency measures, the White House said.

"We believe this is an aggressive goal, but for all three countries, one that we believe is achievable, continent-wide," said Brian Deese, a senior adviser to Obama.

That is a jump from the current collective clean power levels of about 37 percent, and will require the most ambition from the United States, which produces about 75 percent of the countries' power.

About a third of U.S. power now comes from clean energy sources.

Curbing climate-changing carbon emissions has been a priority for Obama as the end of his second and final term in office draws closer.

But his new regulations on coal-fired power plants - the main U.S. tool to reach emissions targets pledged at U.N. climate talks in Paris in December 2015 - were put on hold by the U.S. Supreme Court earlier this year.

The White House believes its Clean Power Plan rules will ultimately survive the challenge. The rules, along with tax credits for renewable power plants, will help the United States do its share to reach the North American goal, Deese said.

He said it would not be necessary for the United States itself to hit the 50-percent mark to achieve the regional target.

Mexico produces less than 20 percent of its power from clean energy, Deese said, noting officials there had already pledged to reach 35 percent by 2024.

Canada produces 81 percent of its electricity from hydroelectric, solar, wind and nuclear power generation, according to the Canadian Broadcasting Corp, which first reported the North American deal earlier on Monday.

At the Wednesday summit, the leaders also will announce new agreements to make it easier and cheaper to trade and transmit clean energy across the continent, Deese said.

Mexico also will join a pledge made earlier this year by Obama and Trudeau to reduce methane emissions by 40 percent to 45 percent by 2015, he said.

(Reporting by David Ljunggren in Ottawa, Roberta Rampton in Washington and Simon Gardner in Mexico City; editing by Alan Crosby and G Crosse)