WASHINGTON - German Chancellor Angela Merkel is expected to urge the United States to take bold action to combat global warming in a speech to a joint session of Congress on Tuesday, a month before a U.N. climate summit.

Merkel, who began her second term in office last week, will meet with President Barack Obama at the White House before giving the first address to the U.S. Congress by a German leader since Konrad Adenauer in 1957.

She signaled in a podcast over the weekend that climate change would be a central theme of her Washington visit, describing it as a global task we cannot afford to push back.

Hopes that countries can agree a binding treaty at the December 7-18 meeting in Copenhagen are dimming and some believe that targeting a deal in 2010 might be more realistic.

A big hurdle is opposition within the U.S. Senate to a domestic climate bill sponsored by the Democrats.

If the Senate is unable to agree on legislation to cut greenhouse gas emissions before the summit, the Obama administration will have its hands tied in Copenhagen and the chances of a deal will erode further.

At a final preparatory meeting in Barcelona on Monday, the United States came under pressure to follow other rich countries and set a 2020 goal for cutting greenhouse gases. The summit's prospective Danish hosts said it could not come empty-handed to Copenhagen.

We need a clear target from the United States in Copenhagen, said the head of the U.N. Climate Change Secretariat, Yvo de Boer. That is an essential part of the puzzle.

SPECIAL RELATIONSHIP

Merkel's speech, timed to coincide with next week's 20th anniversary of the fall of the Berlin Wall, is an opportunity to address U.S. lawmakers directly and drive home a message that the world is watching Washington on the climate issue.

In 2007, Merkel cajoled Obama's predecessor, George W. Bush, into backing a strong G8 statement on global warming, earning the nickname Klimakanzlerin, or Climate Chancellor. But winning over skeptical Senate Republicans may be tougher.

Officials said Merkel's speech would last about 30 minutes and be delivered mainly in German. She is expected to highlight the special postwar relationship between Germany and the United States and Washington's role in helping bring down the Berlin Wall with its tough stance toward the Soviet Union.

Merkel is the only German chancellor to have grown up in communist East Germany, giving her a unique perspective on the Cold War and the events leading up to the toppling of the Wall on November 9, 1989.

In her speech she is also likely to touch on the conflict in Afghanistan and the nuclear showdown with Iran as examples of challenges the West must unite to overcome. All three issues are on the agenda for her talks with Obama.

Western powers are engaged in a cat-and-mouse game with Iran, which has signaled that it wants fundamental changes to a nuclear fuel deal it committed to in talks last month.

The president will want to get her sense on how she sees things with Iran and what needs to be happening here, said a U.S. official, speaking on condition of anonymity.

The United States, Germany and their NATO allies are struggling to forge a new strategy on Afghanistan, where violence is at its worst since the Taliban were ousted in 2001.

Obama is weighing a request from his top commander in Afghanistan to increase U.S. troop levels by 40,000.

Merkel, French President Nicolas Sarkozy and British Prime Minister Gordon Brown have called for a conference early next year to set targets for handing over responsibility for security to Afghan authorities.

(Writing by Noah Barkin; Editing by Chris Wilson)

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