President sticks to big themes of freedom and openness but acknowledges concerns over threats to privacy and drone strikes

Barack Obama called for a renaissance in the shared liberal values that underpin western nations on Wednesday as he announced plans to cut nuclear weapons in a much-anticipated speech in Berlin that also acknowledged unease over privacy and drone strikes.

Speaking at the Brandenburg Gate, in the shadow of historic speeches by Presidents Kennedy and Reagan, Obama stuck to big themes but clearly sought to address concerns in Germany caused by recent revelations of internet surveillance and US drone warfare.

After quoting Immanuel Kant on freedom and his belief "in open societies that respect that sanctity of the individual", the president echoed calls he made during a recent speech in Washington for an ending of America's war on terror.

"Threats to freedom don't merely come from the outside; they can come from within, from our own fears. For over a decade, America has been at war, but much has changed … no nation can maintain its freedom if it does not move beyond mindset of perpetual war."

The president called for tight controls on the "use of new technology like drones and balancing security with privacy" but said he was confident the US could strike the right balance.

Obama: big themes. Photograph: Christof Stache/AFP/Getty Images

Obama also insisted that US surveillance programmes were aimed at "threats to security, not the communications of ordinary persons" and said "they keep people safe in Europe as well as the US".

But he acknowledged there were legitimate concerns over privacy and other hot-button issues such as drones and Guantánamo.

"We must listen to voices that disagree with us, and have a open debate about how we use our powers and remember that government exists to serve the power of individual not the other way around … that is what keeps us different to those on the other side of the wall. That's what keeps us true to our better history," said Obama.

Among the only firm policy statements was a comittment to cut US nuclear weapons arsenals by a third and seek fresh talks with Russia to reduce stocks further.

"We are on track to cut nuke warheads to lowest levels since 1950s … but we have more work to do, so I am announcing [that] we can ensure security of US and allies by reducing our stored weapons by up to one third," said Obama. "I intend to start talks with Russia to move beyond cold war postures."

Speaking to an invited crowd of 6,000 guests, he also hinted at calls for greater German support for US intervention in countries such as Syria.

"We cannot dictate the pace of change in Arab world but we must reject the excuse that we can do nothing to support it," said Obama.

But much of the speech was couched in broad calls for a restoration of the western alliance that helped defeat communism, amid growing fears in Washington that support for Nato and US is waning in Europe.

"There can at times be a complacency among our western democracies," he said. "We face no concrete walls … sometimes there can be a sense that the great challenges have somehow passed and that brings with it a temptation to turn inward."

Obama wipes his brow. Photograph: Christof Stache/AFP/Getty Images

Receiving a cheer for taking his jacket off in sweltering heat and reprising John F Kennedy's "Ich bin ein Berliner" line, Obama called on German people to remember what they shared with America.

"Our alliance is the foundation of global security and our trade the engine of the global economy," said the president.