* Series of talks on missile shield due in coming weeks
* Russia says still demands legally binding guarantees
NATO hopes a U.S. change to global missile defences will dispel Russian concern and foster cooperation on an issue that has long strained relations, alliance Deputy Secretary General Alexander Vershbow said in an interview.
Russia has said U.S. missile shield plans could erode its nuclear deterrent. It has softened criticism since Washington announced on March 16 that it would station 14 missile interceptors in Alaska in response to North Korean nuclear threats and at the same time forgo a new type of interceptor that would have been deployed in Europe.
However, Moscow has said it wants a series of consultations on the new shield set-up and U.S. and Russian defence officials are expected to hold talks on that in the coming weeks.
Moscow has long been at odds with the West over anti-missile defences it has begun to establish in Europe, which both the United States and NATO say are aimed at preventing any attack from Iran and pose no threat to old Cold War foe Russia.
"The change in the U.S. plans ... just simply makes the situation much less ambiguous," Vershbow told Reuters. "There is now no reason for concern that the system going into Europe will have any effect whatever on Russia's strategic deterrent.
"We think there is a real window of opportunity and we hope that the Russians seize it," said Vershbow, who has held talks with senior officials from the Russian foreign and defence ministries as well as President Vladimir Putin's Kremlin.
The skipped interceptors were meant to be able to target long-range missiles, sparking concern in Moscow that they could be used against its intercontinental ballistic missiles.
"On both the NATO-Russia and U.S.-Russia tracks, we hope the dialogue will pick up speed so that we can get at least closer to some kind of a deal on missile defence cooperation," said Vershbow, a former U.S. ambassador to Russia.
"To the extent we are able to make some progress on missile defence, it might also facilitate renewed dialogue on nuclear arms reductions both at the strategic level and the non-strategic level." He said broader NATO-Russia ties would get "a shot in the arm" if progress was made on missile shields.
Moscow has frequently said it is unlikely to go for further cuts in its nuclear arsenal unless Washington satisfactorily addresses its concerns about the defence system Washington has started to deploy in Europe in cooperation with NATO partners.
Russia is also pushing to host a meeting of defence ministers of NATO and Russia in Moscow in May and some in Russia have expressed hope for progress by then.
But Moscow is sticking to its demand for legally binding guarantees that the shield will not be aimed at Russia, a request rejected by NATO and the United States.
Any significant progress may be difficult because of Russian concern that developing NATO infrastructure in central and eastern Europe is tipping the post-Cold War balance of power.
"There are broader political questions that still could remain difficult to resolve," Vershbow said.
"NATO has been very clear that legal guarantees will not be possible but I'm sure we could develop some kind of political framework that would give the Russians the predictability that they are seeking through legally binding guarantees."