BERLIN—Standing before a towering emblem of the Cold War, President Barack Obama called for steep reductions in nuclear weapons through negotiations with the Russians, as a step toward what he conceded was the "distant" goal of eliminating global arsenals.

"We may no longer live in fear of global annihilation, but so long as nuclear weapons exist, we are not safe," Mr. Obama said Wednesday in an address in front of the Brandenburg Gate in his first visit to the German capital as president. "I intend to seek negotiated cuts with Russia to move beyond Cold War nuclear postures."

His public invitation—which included his assessment that the U.S. can cut the number of deployed nuclear weapons by one-third without compromising American security—received a cool reception from Moscow.

Mr. Obama's speech came five years after he visited Berlin and drew a crowd of 200,000 people who wanted a glimpse of the rising young candidate, and 50 years after former President John F. Kennedy showed solidarity with residents of the divided city, declaring "Ich bin ein Berliner."

He sought to link his moral and policy agenda to that of the 35th president. Reciting a less-known phrase from Kennedy's speech in Berlin that day, Mr. Obama said he, too, wants to achieve "peace with justice"—by doing away with nuclear arms, ensuring women have the same opportunities as men and reversing the effects of climate change. He pledged, without offering details, to take new measures to protect the environment.