The White House called Obama’s decision “a sign of his continuing commitment and leadership to find a global solution to the global threat of climate change.”

The president will lay out his goals for reducing the United States’ carbon dioxide emissions by about 17 percent from 2005 levels by 2020. That target reflects climate legislation still pending in Congress. A House-passed bill would slash heat-trapping pollution by 17 percent. A Senate bill seeks a 20 percent reduction, but that number is likely to come down to win the votes of moderate Democrats.

Obama’s commitment to that goal would reverse long-standing U.S. opposition to mandatory emission cuts during eight years of the Bush administration.

The White House also said a half dozen Cabinet officials including Energy Secretary Steven Chu and Commerce Secretary Gary Locke as well as the head of the Environmental Protection Agency — which is preparing regulations to cut greenhouse gases — will take part in the Copenhagen talks. It is the highest profile contingent of U.S. officials to ever take part in international climate negotiations.

The conference had originally been intended to produce a new global climate change treaty on limiting emissions of greenhouse gases that would replace the 1997 Kyoto Protocol. However, hopes for a legally binding agreement have dimmed, with leaders saying the summit is more likely to produce a template for future action to cut emissions blamed for global warming.

At least 75 world leaders will attend. Unlike Obama, most are expected to attend the final days of the Dec. 7-18 conference.

Yvo de Boer, U.N. climate treaty chief, told reporters in Bonn, Germany, Wednesday that Obama’s attendance was critical. He said, “The world is very much looking to the United States to come forward with an emission reduction target and contribute to financial support to help developing countries.”

Former Vice President Gore had urged Obama to make the trip. Gore’s participation in the 1997 Kyoto talks were key to breaking an impasse that threatened the climate talks that eventually produced an agreement by developing countries to cut greenhouse emissions. The United States, however, never ratified the agreement.

Obama’s visit to Copenhagen will be at the beginning of the talks when the conference agenda will be largely ceremonial.

“The Copenhagen climate summit is not about a photo opportunity,” said Kyle Ash, climate policy adviser for Greenpeace USA. “It’s about getting a global agreement to stop climate chaos. President Obama needs to be there at the same time as all the other world leaders.”