By Roberta Rampton and Stephen Brown
BERLIN (Reuters) - U.S. President Barack Obama used a speech in Berlin on Wednesday to call on Russia to revive the push for a world without nuclear weapons, offering to cut deployed nuclear arsenals by a third, but Moscow immediately poured scorn on his proposal.
Speaking in Berlin where John F. Kennedy and Ronald Reagan gave rousing Cold War speeches, Obama urged Russia to help build on the "New START" treaty that requires both countries to cut stockpiles of deployed nuclear weapons to 1,550 each by 2018.
The speech, a day after Obama met President Vladimir Putin at a summit where they disagreed publicly about Syria, was given a frosty reception by Moscow which said it could "not take such proposals seriously" while Washington was beefing up its own anti-missile defenses.
"After a comprehensive review I have determined that we can ensure the security of America and our allies, and maintain a strong and credible strategic deterrent, while reducing our deployed strategic nuclear weapons by up to one third," Obama said.
"I intend to seek negotiated cuts with Russia to move beyond Cold War nuclear postures," he said at the Brandenburg Gate, which once overlooked the Berlin Wall that divided the communist east and the capitalist west.
Russia says U.S. plans for anti-missile defenses harm the goal of arms reduction by requiring Moscow to hold more missiles or lose its deterrent capability.
"How can we take the idea of strategic nuclear weapons reductions seriously when the United States is building up its ability to intercept these strategic nuclear weapons?" Deputy Prime Minister Dmitry Rogozin said.
"These things clearly do not go together. It's obvious that Russia's highest political leadership cannot take such proposals seriously," Rogozin told reporters.
Obama's vision of a "world without nuclear weapons" set out in a speech in Prague in 2009, three months into his presidency, earned him the Nobel Peace Prize. But his mixed results so far have fuelled criticism that the prize may have been premature.
Experts said reducing the nuclear arsenal makes strategic and economic sense. But Mark Fitzpatrick at the International Institute for Strategic Studies said Obama faces major obstacles "including a recalcitrant Russia and a reluctant Senate".
Putin, speaking in St. Petersburg minutes before Obama's speech, made no direct comment but voiced concern about U.S. missile defenses and high-precision weapons. Body language between Obama and Putin was chilly when the two men met at the Group of Eight summit on Tuesday in Northern Ireland.
Moscow sees nuclear deterrents as the safeguard of national security. It is worried about the West's superior conventional weapons and NATO plans for a missile defense system in Europe.
"High-precision conventional weapons systems are being actively developed ... States possessing such weapons strongly increase their offensive potential," said Putin.
The chief of the Russian military's general staff appears reluctant to negotiate a new nuclear deal and Russian foreign policy expert Fyodor Lukyanov described Obama's desire to "go to zero globally" as totally unacceptable in Russia.
Obama will also target reductions in U.S. and Russian tactical nuclear weapons in Europe and host a summit in 2016 on securing nuclear materials and preventing nuclear terrorism. He hosted such a meeting in 2010, a second was held in Seoul in 2012 and Obama will attend a third in The Hague next year.
When they met at the G8 summit, Putin and Obama signed a new agreement on securing nuclear material left over from the Cold War, replacing the 1992 Nunn-Lugar agreement that expired on Monday.
That was "the kind of constructive, cooperative relationship that moves us out of a Cold War mindset", Obama said afterwards.
Early initiatives of Obama's presidency led to the New START treaty plus measures to bolster the Non-Proliferation Treaty and a new effort to secure nuclear materials worldwide, but that push has flagged in the face of political realities.
But Obama said the United States and Russia were on track to cut deployed nuclear warheads "to their lowest levels since the 1950s" and said a framework was being forged to counter what he called Iran and North Korea's "nuclear weaponization".
Iran denies it is seeking nuclear weapons. North Korea has tested nuclear devices.
Obama also wants to see negotiations on a treaty to end the production of fissile materials for weapons.
Experts and advocacy groups described Obama's initiative as "long overdue" and the reduction targets as modest.
"The one-third cuts outlined by the President are but 200-300 warheads fewer than the United States was prepared to agree to during the New START negotiations four years ago," said Daryl Kimball of the Arms Control Association in Washington.
"The U.S. could have gone much lower and maintained deterrence," said Jon Wolfsthal, a former special advisor to the vice president on nuclear security and non proliferation. He saw little chance of success in the face of political opposition.
"Our experience has been that nuclear arsenals - other than ours - are on the rise," said Jim Inhofe, the top Republican on the Senate's Armed Services Committee, pointing to Iran and North Korea.
"A country whose conventional military strength has been weakened due to budget cuts ought not to consider further nuclear force reductions while turmoil in the world is growing."
(Additional reporting by Denis Dyomkin, Jeff Mason, Alexei Anishchuk, Fredrik Dahl and Timothy Heritage; Writing by Stephen Brown and Peter Graff; Editing by Giles Elgood)