MOSCOW -- The United States has effectively canceled the final phase of a Europe-based missile defense system that was fiercely opposed by Russia and cited repeatedly by the Kremlin as a major obstacle to cooperation on nuclear arms reductions and other issues.
Russian officials have so far declined to comment on the announcement, which was made in Washington on Friday by Defense Secretary Chuck Hagel as part of a plan to deploy additional ballistic missile interceptors to counter North Korea. Much of the savings from canceling the extra Europe-based defenses will help fund those added interceptors.
Aides to President Vladimir V. Putin said there would be no reaction until early this week, when they expect to be briefed by American officials.
But Russian news accounts quickly raised the possibility that the decision could portend a breakthrough in what has been a largely intractable dispute between Russia and the United States for years. A headline by the Itar-Tass news agency declared, "U.S. abandons fourth phase of European missile defense system that causes the greatest objections from Russia."
Pentagon officials said those long-standing objections by Russia played no role in the decision to reconfigure the missile interceptor program, which they said was based on the increased threat from North Korea, and on technological difficulties and budget considerations related to the Europe-based program.
"The missile defense decisions Secretary Hagel announced were in no way about Russia," George Little, a Pentagon spokesman, said Saturday.
Still, other Obama administration officials acknowledged potential benefits if the decision is well-received in Moscow, as well as the possibility of continued objections given that the United States is not backing away from its core plan for a land-based missile shield program in Central Europe.
"There's still an absolutely firm commitment to European missile defense, which is not about Russia; it's about Iran these days," said a senior administration official who spoke on the condition of anonymity. "If there are side benefits that accrue with Russia, so be it. But that wasn't a primary driver."
Regardless, some experts said it could help relations by eliminating what the Russians had cited as one of their main objections -- the interceptors in the final phase of the missile shield that might have the ability to target long-range intercontinental ballistic missiles, which are part of Russian's nuclear arsenal.
The Obama administration has sought cooperation from Russia on numerous issues with varying degrees of success. Russia generally has supported the NATO-led military effort in Afghanistan, and has helped to restrict Iran's nuclear program by supporting economic sanctions. But the two countries have been deeply at odds over the war in Syria, and over human rights issues in Russia. Most recently, President Barack Obama has said he would like further reductions in the two countries' nuclear arsenals, something Russia has said it would not consider without settling the dispute over missile defense.
U.S. experts insisted that the Russians' concern over the anti-missile program was exaggerated and that the system would not have jeopardized their strategic missiles, had the final phase been developed. But that Russian concern has now been addressed.
"There is no threat to Russian missiles now," said Steven Pifer, an arms control expert who has managed Russia policy from top positions at the State Department and the National Security Council. "If you listen to what the Russians have been saying for the last two years, this has been the biggest obstacle to things like cooperation with NATO."