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.

“This is a very meaningful shift in policy,” said James G. Stavridis, a retired admiral and the former supreme allied commander of NATO, who is now dean of the Fletcher School of Law and Diplomacy at Tufts University. “It provides a reasonable level of reassurance to jittery allies, although nothing is as good as troops stationed full-time on the ground, of course.”

The amount of equipment included in the planning is small compared with what Russia could bring to bear against the NATO nations on or near its borders, but it would serve as a credible sign of American commitment, acting as a deterrent the way that the Berlin Brigade did after the Berlin Wall crisis in 1961.