BRUSSELS—NATO countries are discussing increasing the number of troops stationed in members bordering Russia and putting them under formal alliance command, part of a new effort to deter aggression from Moscow, according to diplomats and military officers.

Under one plan, the North Atlantic Treaty Organization would have a battalion in Poland and each of the three Baltic states—roughly 800 to 1,000 soldiers in each unit. A more modest version would have a single NATO battalion in the area.

While...