(Adds quotes, Merkel call with Xi)
BERLIN, March 16 (Reuters) - Export powerhouse Germany on Thursday criticised U.S. moves to challenge international treaties as Chancellor Angela Merkel headed to Washington for a first meeting with U.S. President Donald Trump.
Trump has unsettled allies around the world by challenging multilateral trade agreements and other treaties, while accusing Germany, China and others of manipulating their currencies to boost exports.
Such questioning jeopardised Germany's stability, but would also harm the United States in the long-run, German Foreign Minister Sigmar Gabriel told a conference on international law.
He said the new U.S. administration's demand to negotiate only bilateral trade deals posed significant political and economic challenges for Germany as the largest economy in Europe and a key member of the European Union, which negotiates trade deals on behalf of its members.
"That endangers the stability of our country, and in the end, I think it will also harm the stability of the United States," he said.
German leaders hope to revisit plans for a European-U.S. trade agreement in several years, heartened by the fact the Trump has not specifically targeted that potential trade deal while blasting other free trade pacts with Canada and Mexico, and some Asian countries.
They have also said Germany could step into the void left as Washington withdraws from the international stage.
Merkel and Chinese President Xi Jinping agreed in a phone call on Thursday to work together for free trade and open markets, a German government spokesman said.
"They spoke in particular about the conditions to expand electromobility in China which will allow the German auto industry to continue to be successful in the Chinese market," said the spokesman.
Gabriel said Germany would work with the Trump administration to underscore the importance of a international treaties. But it would likely take "many visits to the United States" to get the message across, he added.
Trade will be a key issue when Merkel meets with Trump for over two hours on Friday, followed by a working lunch. The talks are also expected to focus on foreign policy issues ranging from NATO and Russia to Syria, Middle East peace, Iran, North Korea and the European Union.
The German leader will be accompanied by top executives from three German companies, including engineering group Siemens and carmaker BMW.
Trump has threatened to impose tariffs on German carmakers that import into the United States and has criticised Berlin for not spending more on defence. Another source of tension is Germany's 50 billion-euro trade surplus with the United States.
The United States is Germany's biggest export destination, buying German goods and services worth 107 billion euros ($114 billion) last year while exporting just 58 billion euros' worth in return.
It is Germany's third-largest trading partner, just behind China and France. Merkel said German companies employ about 750,000 people in the United States and 1 million to 2 million jobs in the United States depend indirectly on German companies. (Reporting by Andreas Rinke; Writing by Andrea Shalal; Editing by Madeline Chambers and Alison Williams)