WASHINGTON—European leaders pressed Congress and the White House on Tuesday to unite on a plan to combat global warming, even as a Republican boycott forced a delay of votes in a key Senate committee, demonstrating the deep partisan rift.

An emotional plea for action by German Chancellor Angela Merkel in an address before Congress was met with silence from most Republicans, while Democrats stood and applauded.

The Europeans as well as the U.S. were pressured in turn by African nations to do more, at a conference in Spain leading up to next month’s international climate summit in Copenhagen, Denmark.

In Washington, shortly before Merkel spoke in the House chamber, GOP senators on the Environment and Public Works Committee shunned the planned startup of voting on amendments to a 959-page Democratic bill that would curb greenhouse gases from power plants and large industrial facilities. They protested that the bill’s cost to the economy—in the form of more expensive energy and the impact on jobs—had not been fully examined.

The action underscored the difficulties Democratic leaders face in moving climate legislation this year—or even in showing significant momentum ahead of the Copenhagen conference. At that meeting, nations will try to forge an agreement on cutting heat-trapping pollution beyond levels established in 1997 in Kyoto, Japan.

“We all know we have no time to lose,” Merkel said, arguing that at Copenhagen “the world will look to us, to the Europeans and to the Americans” for leadership on setting binding reductions of greenhouse gases. It’s a matter “in the interest of our children and grandchildren and in the interest of sustainable development all over the world,” she said.

“I liked her speech, but I disagree with her completely on the climate comments,” said Sen. John Barrasso, R-Wyo., a sharp critic of the Senate bill.

Merkel made the same plea on climate action earlier in a meeting with President Barack Obama on a day of far-flung developments concerning the contentious climate change issue:

• European Union leaders, also meeting with Obama at the White House, pressed anew for U.S. action. European Commission President Jose Manuel Barroso told reporters that he was worried about the progress being made ahead of the Copenhagen conference and called a climate agreement “a defining moment” for this generation of world leaders.

• The European officials pressed for a larger U.S. contribution to an international aid fund to help developing countries adapt to a warmer world.

• In Barcelona, Spain, African delegates to a preliminary climate conference briefly boycotted the discussions over their concern that industrial nations will not have to make significant enough reductions in greenhouse gases. They ended the boycott after assurances that the issue would be the subject of extended negotiations.

• Former Vice President Al Gore, a leading voice for action on global warming, said he expects Obama to visit the Copenhagen conference to reinforce the country’s commitment.