"It is clear that the European Union can no longer adequately respond to Russia's demonstrations of power, so it is comforting that at least the United States is finally stepping up," Roman Kuzniar, a professor at the Institute of International Relations at the University of Warsaw, said on Tuesday.
Mr. Putin's annexation of Crimea in 2014 and his continued support for pro-Russian separatists in eastern Ukraine - along with provocative incursions into Ukraine's airspace, increased submarine patrols and large-scale military maneuvers near its western borders - have unsettled many of the former Communist states in the region and have led to increasing demands for a concrete Western response. The news from Washington was welcomed by several government officials.
"We appreciate President Obama's decision to boost funding for an increased U.S. military presence on the territory of NATO's front-line allies," the Czech Defense Ministry said in a statement on Tuesday. "The U.S. is the leader of the Atlantic alliance and has an indispensable role in making its collective deterrent sufficiently robust and credible."
Raimonds Bergmanis, the Latvian defense minister, said in a statement on Tuesday: "Deterrence is what we are after, and a decision by the U.S. authorities to preposition equipment in Central and Eastern Europe would send a clear message of resolve and determination."
The news was expected to draw a harsh reaction from the Kremlin and to prompt Mr. Putin to respond with a buildup of his own, although analysts doubted that it would inspire a new arms race.
"Russia will not welcome the strengthening of the American contingent in Europe, at the time when, regardless of the overall political difficulties, there is no risk of a direct military confrontation with NATO," said Igor Korotchenko, editor in chief of the Russian magazine National Defense. "This will make the system in Europe more unbalanced. It is one thing when the Americans deploy their forces in Spain, but it is very different when they deploy them in Poland, Romania or the Baltic States."
Still, Mr. Korotchenko added, "the response will not be hysteric."