WASHINGTON Russia and the United States are "really close" to agreement on a landmark treaty to cut their nuclear arsenals, a senior U.S. arms control official said on Wednesday.
The top U.S. negotiator was headed to Moscow for talks on a replacement for the Cold War-era START I treaty, said Ellen Tauscher, undersecretary of state for arms control and international security.
Formal negotiations will resume in Geneva on January 25, Tauscher told reporters.
"I think we are really close," she said, although she would not predict when the treaty might be signed. "We are in a place where we are working very, very hard."
Forging a replacement for the 1991 START treaty is a key element of U.S. President Barack Obama's efforts to mend troubled relations with Russia, curb global arms proliferation and move toward a world without nuclear weapons.
Tauscher played down the failure to reach a deal by December 5, when START expired.
"Nobody's expectation ever was that this was going to be a lay-up," she said.
After negotiators broke for the Christmas and New Year holidays, Russian Prime Minister Vladimir Putin challenged the United States by saying that its plans for a missile defense system were the main obstacle to an agreement.
Obama moved to placate Russia last year by scrapping plans for missile defense installations in Eastern Europe, and the Kremlin had seemed to accept that the U.S. position that the new treaty must not place restraints on missile defense.
Analysts say the pact would have little or no chance of ratification in the U.S. Senate if it were to encompass missile defense. Tauscher said Washington would stand its ground.
"We have made very clear consistently and repeatedly that this is an offensive treaty and that this does not deal at all with missile defense," she said.
HOPE FOR SIGNING BY MAY
The United States now wants the treaty signed by May to set an example for a conference it hopes will bolster the global Nuclear Non-proliferation Treaty.
"If you and the Russians control 95 percent of the nuclear weapons and you're not reducing, you're going to weaken your hand if you're pressing for tighter measures" to rein in other nations' nuclear programs, said Steven Pifer, a senior fellow at the Brookings Institution.
In July, Obama and Russian President Dmitry Medvedev agreed that the new treaty should cut the number of deployed nuclear warheads on each side to between 1,500 and 1,675.
Despite Putin's remarks, Pifer said he would be surprised if Russia pushes hard on missile defense because it is aware that would likely scuttle chances for Senate approval.
Russia has a pragmatic interest in reaching agreement, he said, because its aging arsenal is likely to fall below 1,500 warheads in the next five or six years anyway.
"So this treaty is their means of assuring that the United States comes down with them," Pifer said.
(Editing by Cynthia Osterman)