By Roberta Rampton and Marcin Goettig
WARSAW (Reuters) - President Donald Trump affirmed U.S. commitment to the defense of NATO allies on Thursday in a Warsaw speech that gently criticized Russia, and said Western civilization must stand up to those "who would subvert and destroy it"
In his second trip to Europe as president and shortly before leaving for a potentially fractious G20 meeting in Germany, Trump appeared to want to soothe U.S. allies after unnerving them in May by failing to endorse the principle of collective defense enshrined in Article Five of the NATO treaty.
As a presidential candidate, Trump called NATO obsolete, but he has since changed his position on the alliance's relevance.
The president also had tough words for Russia on Thursday, though he did not fully endorse allegations, backed by U.S. intelligence agencies, that Moscow interfered in the 2016 presidential election that he won.
Trump meets President Vladimir Putin for the first time face-to-face on Friday in Hamburg, the site of the G20 summit.
"We urge Russia to cease its destabilizing activities in Ukraine and elsewhere and its support for hostile regimes including Syria and Iran, and to instead join the community of responsible nations in our fight against common enemies and the defense of civilization itself," he said.
The Kremlin said Russia was not guilty of any destabilizing activity.
The brief visit to Warsaw, to take part in a regional summit, was billed by the White House as an effort to patch up relations with European allies after a tense NATO summit in May.
Trump was received by enthusiastic crowds on a central Warsaw square, some 15,000 people according to police estimates, many arriving on busses organized by ruling party members of parliament from around Poland.
Trump reiterated his previous criticism of low defense spending levels by many European nations and praised Poland for meeting the alliance's target of spending two percent of economic output on defense.
"To those who would criticize our tough stance, I would point out that the United States has demonstrated not merely with words but with its actions that we stand firmly behind Article 5, the mutual defense commitment," he said to applause.
"Words are easy, but actions are what matters...Europe must do more."
Article five of NATO's 1949 founding charter states that an attack on any member is an attack on all, and allies must render assistance, military if need be.
The stopover was a major diplomatic coup for Poland's conservative government, which has faced mounting criticism from Brussels over its democratic record and a refusal to accept migrants fleeing war in the Middle East.
The administration agrees with Trump on issues such as migration, climate change and coal mining and wants EU institutions to give back some of their powers to national governments.
QUESTION OF SURVIVAL
"We've discussed our mutual commitment to safeguarding the values at the heart of our alliance: freedom, sovereignty and the rule of law," Trump said in a joint press conference after meeting Polish President Andrzej Duda.
In what was likely veiled criticism of the European Union, Trump condemned "the steady creep of government bureaucracy" and cited the importance of national sovereignty.
In his speech at a central square that commemorates the 1944 Warsaw Uprising, the president painted the fight against terrorism, illegal immigration and excessive government powers as an existential one.
"The fundamental question of our time is whether the West has the will to survive...Do we have enough respect for our citizens to protect our borders? Do we have the desire and the courage to preserve our civilization in the face of those who would subvert and destroy it?" he asked.
European and other G20 partners have a view of Western values that does not align with Trump's. German Chancellor Angela Merkel has allowed scores of Syrian refugees into her country, drawing both criticism and praise, and has made fighting global warming a top priority at the summit.
Trump's has decided to pull the United States out of the Paris accord on climate change.
While agreeing that they need to put money into collective defense, European leaders took umbrage at Trump's tone and message in Brussels on his first trip there as president.
Duda for his part said he believed Trump took Poland's security seriously.
In Warsaw, Trump was also meeting other central European leaders as well as heads of state from the Balkans and Baltic states, gathered for a so-called Three Seas summit of countries on the Baltic, Black and Adriatic seas.
(Writing by Jeff Mason and Justyna Pawlak; Editing by Ralph Boulton)