And France, which has reverted under the current Socialist government to a more mistrusting view of NATO and its American leadership, is stretched thin in its military campaigns in Mali, the Central African Republic and North Africa and Syria, let alone patrolling its own streets against terrorist attack.

France is likely to contribute only about 150 soldiers to the new deployments, NATO officials say, after finally agreeing to the idea of forward deployments in Poland after initial opposition. Germany, which six months ago opposed these deployments, agreed in return for efforts at renewed dialogue with Russia. It also agreed to lead one battalion.

So the search goes on for a fourth lead nation. Mr. Stoltenberg is confident it will be found by the summit meeting.

The deployments are important, because these combat battalions are designed not to be simple tripwires, but to be large enough and sufficiently well equipped to do an invader real damage. Then they can be reinforced more quickly with the enhanced rapid-reaction force and — another NATO and American decision – to station another United States armored combat brigade of around 5,000 soldiers in Europe (for a total of three) and to pre-position its heavy equipment like tanks and artillery.

Poland is demanding that some of that equipment be pre-positioned on its territory, but for the moment, most of it will go to Germany, Belgium and the Netherlands, which have storage and transport facilities dating from the Cold War.

Only now, in fact, is NATO actually surveying the infrastructure — the bridges, roads and railways — of relatively newer member states in Central and Eastern Europe, not having judged it necessary before to plan how to quickly reinforce them in case of a Russian invasion. Pre-positioning in Eastern Europe would currently require large sums for capital investment to build special new warehouses and infrastructure, Mr. Lute said.