RIGA, Latvia — In a significant move to deter possible Russian aggression in Europe, the Pentagon is poised to store battle tanks, infantry fighting vehicles and other heavy weapons for as many as 5,000 American troops in several Baltic and Eastern European countries, American and allied officials say.

The proposal, if approved, would represent the first time since the end of the Cold War that the United States has stationed heavy military equipment in the newer NATO member nations in Eastern Europe that had once been part of the Soviet sphere of influence. Russia’s annexation of Crimea and the war in eastern Ukraine have caused alarm and prompted new military planning in NATO capitals.

It would be the most prominent of a series of moves the United States and NATO have taken to bolster forces in the region and send a clear message of resolve to allies and to Russia’s president, Vladimir V. Putin, that the United States would defend the alliance’s members closest to the Russian frontier.

After the expansion of NATO to include the Baltic nations in 2004, the United States and its allies avoided the permanent stationing of equipment or troops in the east as they sought varying forms of partnership with Russia.