Speaking at Berlin's iconic Brandenburg Gate, President Obama called for a one-third reduction of the world's nuclear stockpiles. (Associated Press/The Washington Post)

President Obama on Wednesday called for reducing the number of deployed U.S. strategic nuclear warheads by one-third if the Russian government agrees to a similar cut, reviving a goal outlined early in his presidency to work toward a world without nuclear weapons.

Obama’s proposal, which met with a cool reception in Moscow, came during a much-anticipated speech here that sought to shake Western nations from complacency that he said has taken hold since the end of the Cold War.

Speaking at the Brandenburg Gate, a historic backdrop for U.S. presidents, Obama said the dissolution of the Soviet Union has brought “a sense that the great challenges have somehow passed.”

Arguing against that notion, he cited climate change, which he called “the global threat of our time,” international terrorism, poverty and intolerance as challenges that only collective action by the United States and its European allies can solve.

“People often come together in places like this to remember history, not to make it,” Obama told an audience of 4,500 invited Germans, who filled Pariser Platz on the eastern side of the Brandenburg Gate. “But I come here today, Berlin, to say complacency is not the character of great nations. Today’s threats are not as stark as they were half a century ago. But the struggle for freedom and security and human dignity, that struggle goes on.”

Pedestrians in Cologne, Germany, discussed their sentiments towards the American president, his visit to their country and his surveillance programs. (Gabe Silverman/The Washington Post)

Unlike his call for a “new beginning ” with the Muslim world in a speech in Cairo soon after he became president, Obama’s remarks in Berlin were confined to safe political ground. They also exposed the gulf between his ambitious rhetoric and the more modest reality of his foreign policy, which has been less bold in some cases than what he demanded here.

Obama’s half-hour address received a polite, if far from electric, response from the sweltering crowd, who during a festival-like pre-speech program were treated to live violin renditions of music by Michael Jackson, Bruce Springsteen and Beethoven.

The last U.S. president to speak at the Brandenburg Gate was Bill Clinton, who in 1994 addressed Berliners from the gate’s east side. In 1987, President Ronald Reagan chose the setting of the gate, then on the far side of the Berlin Wall, to call on Soviet leader Mikhail Gorbachev to “tear down this wall.” Obama’s address, though, was written to mark the 50th anniversary of President John F. Kennedy’s message of solidarity to Berliners, delivered at another site along the wall just two years after it was built.

For Obama, the speech was also a return to a venue that helped define his 2008 candidacy and the hope it represented for a new style of American leadership after the George W. Bush administration, which saw Europe as more of an obstacle than an ally on national security challenges after the Sept. 11, 2001, attacks.

In 2008, Obama spoke to an estimated crowd of 200,000 people in Tiergarten Park, not far from the Brandenburg Gate. Still highly popular here, Obama nonetheless has seen his star power fade across a once-worshipful Europe.

His expansion of drone warfare, his cautious approach to the Syrian civil war, the failure to close the military prison at Guantanamo Bay, Cuba, and the recent disclosure of the National Security Agency’s vast secret data-collection effort have disillusioned many Europeans and, to a lesser degree, their more pragmatic political leaders.

The NSA revelations resonate particularly among Germans, given their Cold War history. Obama addressed those concerns in his speech, warning that “peace with justice depends on our ability to sustain both the security of our societies and the openness that defines them.”

“Our current programs are bound by the rule of law, and they’re focused on threats to our security — not the communications of ordinary persons,” he said, reading from a paper copy of his speech because the teleprompter at the site was broken. “They help confront real dangers, and they keep people safe here in the United States and here in Europe. But we must accept the challenge that all of us in democratic governments face: to listen to the voices who disagree with us.”

Merkel, raised in East Germany where the Stasi secret police spied intensively on residents, has expressed anger over the program, and she told reporters Wednesday that she had raised her concerns in a meeting with Obama before his speech.

“Although we do see the need to gather information, we also see the need for proportionality,” Merkel said during a news conference with Obama. “This is why an equitable balance needs to be struck.”

The president’s call for further reductions in deployed strategic nuclear warheads from levels approved under the three-year-old New START agreement echoed his speech from Hradcany Square in Prague a few months into his presidency, when he called for a world free of nuclear weapons.

Obama signed New START in April 2010 with Russia’s then-President Dmitry Medvedev, now prime minister. The agreement, ratified by the U.S. Senate later in the year, limits the number of deployed strategic nuclear warheads to 1,550, a two-thirds reduction from the level set by the original START treaty signed two decades earlier.

Obama also called Wednesday for a cut in the number of deployed tactical nuclear warheads in Europe and pledged to work with European allies and the Russia­n government to find ways to do so.

Moscow has long argued that it cannot negotiate strategic or tactical arms reductions without bringing the U.S. missile-defense shield into the discussion. Russian experts are also concerned that deep cuts in the two nations’ nuclear arsenals could tempt other nuclear powers — primarily China — to try to catch up.

“It is necessary to involve other countries possessing nuclear arms in the process of nuclear potential reduction, as well,” Yuri Ushakov, President Vladimir Putin’s foreign policy adviser, said Wednesday at a Moscow briefing.

“The current situation is far from what it was in ’60s and ’70s, when only the United States and the Soviet Union discussed nuclear arms reduction,” Ushakov added. “It is necessary to look at this broader issue now and, naturally, to expand the circle of possible participants.”

Ushakov said the government would not have a detailed comment on Obama’s proposal until it has a chance to study it. But he said ­Putin would oppose any move that would be “a violation of the balance in the system of strategic deterrence or a decline in the efficiency of Russian nuclear forces.”

Natasha Abbakumova in Moscow and Will Englund in St. Petersburg contributed to this report.