The centerpiece of Barack Obama's overseas tour comes Thursday in Berlin when the Democratic presidential candidate gives the only public foreign policy speech of his trip to an Obama-mad crowd of Germans who see him as another John F. Kennedy. He's in a country and a continent making no secret it is ready for change.

"Germans have a great desire to see this as a historic moment," says Bastian Hermisson of the Heinrich Boll Foundation, who estimates that 100,000 will turn out for the speech. "His message that people can hope the world can change for the better – that resonates. The excitement is a sign that we still feel the US is a relevant force, an influence for better or worse."

On his much-scrutinized world jaunt to listen and learn, the Illinois senator is visiting a city at the heart of America's traditional alliance after visits to Afghanistan and Iraq, where the US-Europe relationship is most at risk for reasons of war, oil, and security.

Berlin, twice rebuilt in the 20th century, has symbolic significance, experts say – both for Europe's past and its future. Germany is regarded as the political epicenter of Europe, strategically located between East and West. America may cherish its relations with Paris and London, where Obama travels next, but to move Europe as a whole will require the next president to bolster ties with Berlin, experts say.

"In Berlin, his speech is to Europe, not just to Germany," says Dan Hamilton, director of the Center for Transatlantic Relations at the School of Advanced International Studies (SAIS) in Washington. "It used to be that for the US, the problems were Europe's divisions. Today, the challenge is unity. Berlin reflects this in a way no other city in Europe does."

This city, with its plethora of historical sites, reflects many fears and hopes of the new Europe: Berlin has the largest Turkish population outside Turkey. New immigrant groups mean that in some schools, very little German is spoken. Russian-language newspapers abound in the subway press stands. There are fears of a rising China, and, closer to home, angst about rapidly depopulating cities in the old East.

Berlin is special in the American framework, too: the place where fascism peaked and was defeated; ground zero for the fight over the political values of democracy and communism, for Kennedy's "Ich bin ein Berliner" speech, and the fall of the Berlin Wall. Today it is where East meets West in a vastly freer but more complicated world.

Obama is expected to stress that an America under his leadership would not act unilaterally, will close Guantánamo, be newly cooperative with Europe on climate change and energy. But the presumptive nominee is also expected to add a note of realism, saying that a productive new relationship will require more of Europe – in Afghanistan, and even in Iraq.

Dr. Hamilton, a former deputy assistant secretary of State, anticipates something like, "If Europe and the US stick together, they represent a core group that can get things done in this world. If we don't work together, things don't get done. Iraq and [the] Kyoto [Protocol] are examples."

"The guy needs to demonstrate a willingness to move toward a multilateral approach," says François Heisbourg, head of the Paris-based Foundation for Strategic Research. "I don't think the Europeans expect a detailed foreign policy speech. They want to know if he's a quick learner, does he understand how serious security policy is?"

His audience isn't likely to be hard to win over. Obama may be taking political heat at home, and he's run into a local spat over the location of the Berlin speech. But Germans on both the left and right don't seem to care: 76 percent of Berliners would vote for him, and he's been dubbed by influential news magazine Der Spiegel as "the president of the world." He could "stand on his head" and it wouldn't matter, said one media critic.

Obama originally sought to speak at the historic Brandenburg Gate, but Chancellor Angela Merkel disapproved. "No German candidate for high office would even think of using the National Mall [in Washington] ... for a rally because it would not be seen as appropriate," said spokesman Thomas Steg.

The alternative venue, a famous winged victory column not far away – the Siegessäule featured in the hauntingly beautiful Wim Wenders film "Wings of Desire" – will allow cameras to still frame Obama with the Gate behind.

Obama will, however, meet with Mrs. Merkel. Born and raised in East Germany and fluent in Russian, she is expected to brief him on why Europe has a different take on Moscow. The next US president will have to deal with the thorny question of NATO expansion into Georgia and Ukraine next year – opposed by Germany, but broadly supported by both US parties.

Karen Donfried, vice president of the German Marshall Fund in Washington, argues that Obama's upside in Europe is his ability to inspire. "He's an inspirational individual and that may be important when it comes to offering a vision that asks Europeans to do more. Currently there's a disconnect between policy elites and the public in Europe."

Obama's post-cynical style "makes it possible to have faith in politics," agrees Norbert Rottgen, of Merkel's conservative CDU party.

The potential downside, Dr. Donfried says, would take place if Senator McCain defeats Obama. "The Europeans all think Obama is already elected, they think he will win. If he doesn't, it's going to be a huge letdown in Europe."