By: Julian E. Barnes

July 10, 2016 6:52 a.m. ET

WARSAW—With its Warsaw summit concluded and approval by Western leaders for a deterrent force for the Baltic region gained, NATO’s military brass now must work on the operational details of where to put the troops, how to use them and how to avoid a dangerous accident while operating near growing Russian forces.

The political leaders of the North Atlantic Treaty Organization will also have to explain its moves to Russia. Alliance ambassadors are due to square off against Alexander Grushko, Russia’s Ambassador to NATO on Wednesday. Mr. Grushko has promised to raise tough questions on the alliance’s military activity.

Coming out of the summit, there are some critical tasks for the alliance ahead, including hammering out its relationship with the European Union in the central Mediterranean, working out how to put together a Black Sea fleet, and setting up and positioning the deterrent force of up to 4,000 troops in Poland and the Baltic States.

U.S. Army Gen. Curtis Scaparrotti, the newly installed Supreme Allied Commander Europe, has been tasked with creating the new military plans for the deterrent force—and putting in place the safeguards to ensure that the stepped-up NATO deployment doesn’t result in inadvertent confrontation with Russia.

The Baltic region has been a recent friction point, with some close encounters between Russian aircraft and U.S. ships and planes. U.S. officials have said that Russian pilots have been unsafe and unprofessional, while Russia has said NATO allies are creeping ever closer to its Kaliningrad exclave.

One key question for the NATO commander is how to oversee the multinational battalions. Gen. Scaparrotti said he is keen on designing a command structure that can react quickly, moving from a training exercises to a crisis response posture with ease. That will mean keeping them under NATO command but also integrating them with commanders from Poland, Lithuania, Latvia and Estonia, who are hosting the units, he said.

“The command structure has to be agile enough that from peacetime to provocation to conflict it is a natural transition,” Gen. Scaparrotti said in an interview. “Because the environment we are in today, time is a factor.”

Gen. Scaparrotti said locating the NATO troops will be done in consultation with the U.S., U.K., Germany and Canada who are providing the forces, and the host nations, to make sure they fit in with the overall defense of the countries. Those meetings will begin shortly, he said.

The U.S. will contribute a 1,000 troop strong battalion, likely from the Germany-based 2nd Cavalry Regiment, to the NATO force in Poland, according to U.S. officials. Polish officials have pushed for the force to be located in the Suwalki Gap, the stretch of Polish border between Kaliningrad and Belarus.

NATO and U.S. officials have identified the Suwalki Gap as a critical strategic area to keep open in the event of rising tensions with Russia, but one which could be cut off by Russian missile forces.

Gen. Scapparotti said while he wanted to find the right tactical locations for the deterrent force, it was key not to pin the four battalions in garrisons waiting for a fight that hopefully never comes. “We want to make sure it is a ready force, which means they have to train,” he said. “We want them to be combat ready, because that is part of deterrence.”

The focus of the training, he said, will be the high-end threats a NATO force could face on the alliance’s east flank.

How relations between NATO and Moscow play out in the coming months will “depend a lot on Russian behavior,” and whether Mr. Putin helps implement the peace deal in Ukraine, said former U.S. Secretary of State Madeleine Albright, who was meeting with officials and defense experts on the sidelines of the Warsaw summit.

She said Mr. Putin has escalated tensions with NATO as a result of Russian economic problems. “When your country is not doing well there is also a need to have an enemy,” Ms. Albright said.

For some U.S. and allied officials the nightmare scenario is that larger numbers of Russian and allied land, naval and air forces conducting drills in close proximity could lead to either side misreading an exercise and seeing instead an offensive action.

Such misunderstandings happened during the Cold War, and while NATO leaders repeatedly stress there is no return to that historical period, some officials worry that crisis-creating accident is a real possibility.

The defense against that, officials said, is continuing efforts to be transparent with Russia.

“Communication is important, it will help us understand each others’ intent and most importantly make sure we don’t have a miscalculation or accident in areas we have forces in close proximity,” Gen. Scaparrotti said.

That will begin at Wednesday’s meetings with Mr. Grushko, which are taking place at the insistence of Germany and other allies.

Russian officials declined to comment on the results of the NATO summit, but a spokeswoman said Sunday they were still studying the alliance’s pronouncements.

Canadian Minister of Foreign Affairs Stéphane Dion will visit Latvia on Monday, as Canada prepares to send its forces to the country.

Mr. Dion said that the much of the same transparency NATO applies to its exercise will also apply to its forward forces. He said Canada intends to let Russia observers see its battle group “as much as possible.”

“We don’t want escalation and it must be communicated clearly to Russia,” Mr. Dion said. “The new government in Canada wants to be strong on deterrence and strong on dialogue.”

Mr. Dion said Canada wants to eventually find a partner within Moscow once again, though he acknowledged in the short term, the adversarial relationship will remain.

But, Ms. Albright said, there is no question the alliance is coming out of the summit on a new footing.

“There will be an attempt to have a dialogue with the Russians, to really find areas we can operate together,” she said. “At the same time there is a sense that there will be a real attempt to deal with Russian provocations.