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 enclave 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.