BERLIN (Reuters) - No country can solve the world's problems on its own and governments can achieve more for their nations if they work together closely, German Chancellor Angela Merkel said on Wednesday.

Germany holds the presidency of the G20 leading economies this year, a platform Merkel wants to use to safeguard multilateral cooperation after U.S. President Donald Trump questioned international alliances and obligations and insisted on putting "America first" in his policies.

Speaking at a meeting of female lawmakers from her conservative CDU/CSU bloc, Merkel said she would use her speech at the Munich Security Conference on Saturday to defend the idea of multilateral cooperation.

"No country can solve the problems alone, joint action is more important," Merkel said.

The center-right leader, who faces a federal election in September, added she was convinced that all governments would achieve more for their own country if they worked together instead of isolating themselves.

Merkel said it was a good sign that the new U.S. administration was sending a strong delegation to this year's security conference, a three-day meeting which starts on Friday.

U.S. Vice President Mike Pence and Defense Secretary James Mattis are expected to take part with European allies seeking clarity on the Trump administration's foreign policy strategy and its stance toward Russia.

The Munich conference has become one of the world's most important foreign and security policy gatherings. Participants will discuss the future of transatlantic relations, NATO and the EU, the Ukraine crisis, ties to Russia and the war in Syria, according to the conference's chairman Wolfgang Ischinger.

(Reporting by Michael Nienaber; Editing by Hugh Lawson)