On climate change, Merkel was expected to press Obama to back a European Union goal of limiting increases in global average temperatures to no more than two degrees Celsius.
But the chancellor, whose visit coincided with a vote in the House of Representatives on a bill capping carbon emissions, went out of her way to praise the US legislation, which Obama supports, and its potential to boost UN negotiations in Denmark in December.
"It should not be underestimated what sort of opportunity this brings to us to come to a good, a sustainable result during the Copenhagen conference," she said.
President Barack Obama scored a major victory on Friday when the House of Representatives passed legislation to slash industrial pollution, which is blamed for global warming.
The Democratic-controlled House passed the climate change bill, a top priority for Obama, by a vote of 219-212. As has become routine on major bills in Congress this year, the vote was partisan, with only eight Republicans joining Democrats in approving the bill. Forty-four Democrats voted against it.
The climate change legislation still must get through the Senate. Senators were expected to try to write their own version, but prospects for this year were uncertain.
After the House vote, Senate Majority Leader Harry Reid said he hoped the Senate would pass a bill "this fall".
Obama praised the House for taking "historic action" and urged the Senate to act. "It's a bold and necessary step that holds the promise of creating new industries and millions of new jobs, decreasing our dangerous dependence on foreign oil," Obama said.
With the House action, Obama will be able to tout significant progress toward tackling global warming after years of foreign countries criticising Washington for not participating in international efforts.
The bill requires that large US companies, including utilities, oil refiners, manufacturers and others, reduce emissions of carbon dioxide and other gases associated with global warming by 17% by 2020 and 83% by 2050, from 2005 levels.
They would do so by phasing in the use of cleaner alternative energy than high-polluting oil and coal.
At the core of the bill, which is around 1,500 pages long, is a "cap and trade" programme designed to achieve the emissions reductions by industry.
Under the plan, the government would issue a declining number of pollution permits to companies, which could sell those permits to each other as needed.
'Biggest job-killing bill'
But Republicans said the bill was a behemoth that would neither effectively help the environment nor improve an economy reeling from a deep recession.
House Republican leader John Boehner called the measure "the biggest job-killing bill that has ever been on the floor of the House of Representatives".
Representative Joe Barton, the senior Republican on the Energy and Commerce Committee that played a key role in the bill, said it would set unrealistic targets for cutting carbon pollution. "You would have to reduce emissions in the United States to the level that we had in 1910," Barton said.
Both predicted higher prices for energy and other consumer goods and more US jobs being shipped abroad, as companies try to avoid the tough pollution-control requirements. Democrats said consumers mostly would be protected from price hikes.
Even though climate change - with its threat to polar ice caps and animal and plant species - is a global problem, much of the debate in Congress broke along regional geography, pitting Midwestern and Southern states heavily reliant on dirty coal against coastal areas, where cleaner energies are more available.
(EurActiv with Reuters.)