WASHINGTON — Russia is preparing to send as many as 100,000 troops to the eastern edge of NATO territory at the end of the summer, one of the biggest steps yet in the military buildup undertaken by President Vladimir V. Putin and an exercise in intimidation that recalls the most ominous days of the Cold War.

The troops are conducting military maneuvers known as Zapad, Russian for “west,” in Belarus, the Baltic Sea, western Russia and the Russian exclave of Kaliningrad. The drills will feature a reconstituted armored force named for a storied Soviet military unit, the First Guards Tank Army. Its establishment represents the first time since the collapse of the Soviet Union that so much offensive power has been concentrated in a single command.

The military exercise, planned for many months, is not a reaction to sweeping new economic sanctions on Russia that Congress passed last week. So far, Russia has retaliated against the sanctions by forcing the expulsion of several hundred employees in American diplomatic posts in the country.

But the move is part of a larger effort by Mr. Putin to shore up Russia’s military prowess, and comes against the backdrop of an increasingly assertive Russia. Beyond Russia’s interference in the 2016 presidential election in support of the Trump campaign, which has seized attention in the United States, its military has in recent years deployed forces to Syria, seized Crimea and intervened in eastern Ukraine, rattled the Baltic States with snap exercises and buzzed NATO planes and ships.