Gathered at a summit in Lisbon, leaders of the 28 North Atlantic Treaty Organization states formally committed to a system aimed at protecting the United States and Europe from attack, and offered Russia a chance to collaborate in planning and operations. NATO leaders, who expect Russia to react positively, hope the agreement will lead to cooperation in areas where they could benefit from Moscow's help, including the war in Afghanistan, nuclear nonproliferation and the standoff with Iran.
President Obama told reporters the administration looked forward to working with the Russians "to build our cooperation with them in this area as well, recognizing that we share many of the same threats."
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Yet efforts to develop joint missile defense systems with Russia have fallen apart before, and officials acknowledged that political and technical hurdles remain.
The announcement came near the end of a difficult week for the president. Obama is seeking to bring another key piece of his effort to rebuild relations with Russia — a treaty to reduce nuclear arms stockpiles — to a vote in the Senate before the end of the year. But Senate Republicans, whose numbers will increase in the new Congress that convenes in January, declared this week that there wasn't enough time, prompting pushback from the White House.
The NATO summit, which concludes Saturday, is also focusing on policy on Afghanistan. Member countries are expected to accept a plan to turn security responsibility over to Afghan forces by 2014, a tacit acknowledgement by the Obama administration that the conflict is proving far more difficult than hoped.
Administration officials say they fear that failure to ratify the New START nuclear arms treaty could cause Russia to pull back on its overtures to the West, starting with cooperation on military issues.
NATO has been struggling to knit Russia into a broad security arrangement since the end of the Cold War, with little to show for it. Relations suffered after Russia sent military forces into pro-Western Georgia, a former Soviet republic in the Caucasus region, two years ago.
The West's plans for a missile defense system in Europe have long been a threat to relations. Russia fought strenuously against President George W. Bush's plan to base missile defense interceptors and radar installations in Poland and the Czech Republic, fearing it would be the first step toward a vast system that could neutralize Russia's still-huge nuclear arsenal.
NATO's acceptance of a missile defense system is itself significant, given the strong resistance in Europe to Bush's plan. But European resistance has softened, in part because of growing concerns over the potential nuclear threat from Iran.
The new system will be tied to missile defense networks in the United States. Some of its components may not be in place until 2020.
Russia is initially expected to build a parallel system that would share early-warning data on missile threats; later, the systems could be more fully integrated, officials say.
Sergei Prikhodko, foreign policy advisor to Russian President Dmitry Medvedev, said Medvedev would address the issue in Lisbon on Saturday. Prikhodko said creating a joint system was realistic and "a very simple process" but that Russia wanted to be regarded as a full partner.
"We would like the idea of full-fledged joint participation … to be reflected in some way in the document," he said.
Russia's new attitude toward the plan stems in part from the fact that the system would rely on smaller mobile missiles rather than the larger missiles in fixed ground sites proposed in Bush's plan — which Russia regards as more of a threat to its own missiles.
U.S. officials say Russian resistance to missile defense has been fading for other reasons as well.
Russian leaders have concluded that the United States and allies are going to build a missile defense system "with them or without them," so they would be better off cooperating, Gary Samore, the top White House official on nonproliferation, told an audience at the Nixon Center in Washington on Thursday.
In addition, Russia has likewise become "more nervous" about Iran, he said.
Even so, obstacles remain. Russia has resisted the idea of naming Iran as a target of any joint missile defense system. There may be technical hurdles, analysts say, and objections from Eastern European countries that are wary of inviting Russia too far inside the NATO fold.