By Thomas Escritt and Matthias Sobolewski

BERLIN (Reuters) - U.S. President Donald Trump called Germany's trade and spending policies "very bad" on Tuesday, intensifying a row between the longtime allies and immediately earning himself the moniker "destroyer of Western values" from a leading German politician.

As the war of words threatened to spin out of control, Merkel and other senior German politicians stressed the importance of Germany's Atlantic ties, with Foreign Minister Sigmar Gabriel suggesting the spat was just a rough patch.

Trump took to Twitter early in the day in the United States to attack Germany, a day after Chancellor Angela Merkel ramped up her doubts about the reliability of Washington as an ally.

"We have a MASSIVE trade deficit with Germany, plus they pay FAR LESS than they should on NATO & military. Very bad for U.S. This will change," Trump tweeted.

The tit-for-tat dispute escalated rapidly after Trump, at back-to-back summits last week, criticized major NATO allies over their military spending and refused to endorse a global climate change accord.

On Sunday, Merkel showed the gravity of her concern about Washington's dependability under Trump when she warned, at an election campaign event in a packed Bavarian beer tent - that the times when Europe could fully rely on others were "over to a certain extent".

Those comments, which caused shock in Washington, vented Europe's frustration with Trump on climate policy in particular. And while German politicians sided with Merkel, Foreign Minister Sigmar Gabriel signaled that it was time for cooler heads to prevail.

TIT-FOR-TAT, FROM TENT TO TWITTER

"The United States are older and bigger than the current conflict," he said, adding that relations would improve. "It is inappropriate that we are now communicating with each other between a beer tent and Twitter," he said in Berlin.

Merkel had already begun finessing her message on Monday, stressing that she was a "convinced trans-Atlanticist", a message she repeated after a meeting with visiting Indian Prime Minister Narendra Modi in Berlin.

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But Martin Schulz, leader of Gabriel's center-left Social Democrats, was less emollient earlier in the day when he told reporters Trump was "the destroyer of all Western values". He added that the U.S. president was undermining the peaceful cooperation of nations based on mutual respect and tolerance.

In Rome, Italian Prime Minister Paolo Gentiloni said he agreed with Merkel that Europe needed to forge its own path.

"This takes nothing away from the importance of our trans-Atlantic ties and our alliance with the United States. But the importance we put on these ties cannot mean that we abandon fundamental principles such as our commitment to fight climate change and in favor of open societies and free trade," he said.

(Additional reporting by Steve Scherer in Rome; writing by Paul Carrel; editing by Michael Nienaber/Mark Heinrich)