By Gabriela Baczynska

GDANSK, Poland, June 16 (Reuters) - The leaders of Germany and Poland crowned an improvement in ties on Monday with pledges of cooperation and a walkabout in the Baltic port of Gdansk, a city once the cause of tension between the neighbours.

German Chancellor Angela Merkel greeted local well-wishers with "Dzien Dobry", Polish for "Good Day", on her first official trip to Poland since centrist Donald Tusk became prime minister after winning elections last autumn.

"The Chancellor and I are convinced our efforts to bring our relations to the right level of trust and cordial cooperation are bringing results," Tusk told a joint news conference.

"On issues such as history, cooperation in the European Council and the climate package, we are more and more often finding common ground," he said before the two leaders took a stroll in the old town of Gdansk, known in German as Danzig.

The convivial tone contrasted strongly with that of the previous conservative government of Jaroslaw Kaczynski, whose twin brother Lech remains Poland's president.

Critics of the Kaczynskis accused them of fomenting anti-German sentiment linked to Nazi Germany's invasion of Poland in 1939. Bilateral strains acquired a personal flavour when a German paper billed the pair as "Poland's new potatoes".

The choice of Gdansk for the Merkel-Tusk talks underlined the leaders' desire to lay historic tensions to rest.

The city has been both Polish and German at different times in its long history. Warsaw's refusal to hand it to German dictator Adolf Hitler in the 1930s helped trigger the Nazi invasion of Poland and the start of World War Two.

MUSEUM DIPLOMACY

Tusk, a native of Gdansk, said he and Merkel discussed Polish plans to build a World War Two museum in the city.

"As soon as the concept (of the museum) is ready we will start inviting European countries, Germany among them, to cooperate," he told the news conference.

Germany's League of Expellees has said the Polish project should not become a substitute for their vision of a separate museum. Eastern European critics of the League's plan fear it may portray Germans as victims of a war which the Nazis started.

"If we are asked we would gladly participate (on the Gdansk museum). I think this is very exciting, a very good idea that we can all learn from," Merkel said.

Merkel cited plans for a joint German-Polish history book as a further example of efforts to promote mutual understanding.

Tusk said Merkel had backed a joint Polish-Swedish proposal for an Eastern Partnership to help prepare ex-Soviet repulics such as Ukraine for eventual membership of the European Union.

Poland, which with strong German backing joined the EU in 2004, has emerged as a robust advocate for the bloc's further eastern expansion into former Soviet territory.

Merkel and Tusk also discussed Warsaw's concerns that EU plans to cut greenhouse gas emissions are too ambitious and could harm Poland's economic growth. Poland derives 95 percent of its energy from environmentally-unfriendly coal.

"The Chancellor's declaration that we will cooperate on this issue is a very important sign for us," Tusk said.

Poland has previously said it is preparing scenarios to prevent the full auctioning of carbon dioxide emission permits due to start in 2013.

"We will exchange ideas on this, we must help each other," said Merkel. (Additional reporting by Noah Barkin in Berlin; Writing by Gareth Jones; Editing by Matthew Jones)

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