WASHINGTON — President Obama and President Xi Jinping of China said Thursday that they would sign the Paris Agreement on climate change on April 22, the first day the United Nations accord will be open for government signatures.

Officials cast the announcement as a statement of joint resolve by the world’s two largest greenhouse gas polluters, even though there are doubts about whether the United States can meet its obligations under the agreement.

In February, the Supreme Court temporarily blocked an Obama administration regulation to curb greenhouse gas pollution from power plants, the centerpiece of Mr. Obama’s climate change policy and the major way for the administration to meet its targets under the Paris accord.

The two world leaders made the announcement on the sidelines of a nuclear security meeting in Washington.