Fielding new systems to defend against a cruise missile threat, rather than upgrading the existing ballistic missile defense, may also prove more politically palatable. “If NATO is to update its systems, it may undermine its years-long claim that the launchers were never meant to counter Russia,” said Bruno Lété, a defense analyst in the Brussels office of the German Marshall Fund of the United States.

But many Europeans see themselves as in the line of fire with the new Russian cruise missile deployments, he said. “There is a clear incentive for NATO to see if they can upgrade the existing systems to counter Russian intermediary missiles,” Mr. Lété said. “From a military perspective, this would be a relatively simple, decisive and cost-effective step.