The push for improved defenses is fueled by Russia’s fielding of a new class of missiles as well as the expected demise of the treaty — a casualty of deteriorating relations between Russia and the United States. Eastern European countries, particularly Poland and the Baltic states, believe they are under growing threat of nuclear bullying by Moscow and have been eager to see the alliance develop new defenses.

Based on intelligence from multiple allied agencies, NATO countries have forged a consensus that the new Russian nuclear-capable cruise missiles pose a threat. The missiles, some American and European analysts fear, could give Moscow significant leverage, using the threat of attack to force other countries to de-escalate or give in to Russian demands during a crisis.

The relationship between Russia and the West has spiraled downward since Moscow’s 2014 annexation of Crimea. Russia’s destabilization of Ukraine forced the alliance to reinforce its eastern flank with new troop deployments and military exercises. Moscow responded with its own military upgrades, ultimately including the deployment of a new class of ground-based cruise missiles that the West said violated the I.N.F. treaty. Russia’s election interference, its intervention in Syria and the attempted poisoning of a former Russian intelligence officer in Britain further heightened tensions.

Any move by NATO to redirect its missile defenses or expand its system with new capabilities could be a tipping point. Russians have never believed the alliance’s denials that its interceptor system would not eventually be used to shoot down Russian missiles. The system has remained a persistent irritant for Moscow, which questioned why the alliance still needed it after Iran agreed in 2015 to pause its nuclear enrichment program and threatened to direct missiles at the alliance interceptor sites.

Officials at Russia’s NATO embassy did not return requests for comment.

Last week, allied defense ministers approved an examination of potential responses to the Russian deployment of so-called SSC-8 cruise missiles, the weapon NATO accuses Moscow of deploying in violation of the treaty, according to three NATO officials. They include expanding existing deterrence exercises and publicizing the alliance’s nuclear exercises, which are highly secretive. Drawing more attention to the allied nuclear exercises and arsenal would help deter Moscow’s use of its own weapons, some officials think.

NATO will probably need to examine more broadly what defenses it needs against the cruise missiles. Such work, if approved this year, would include exploring whether it can upgrade its Aegis Ashore radar and interceptor sites in Romania and Poland and looking at new radar or air defense capabilities against the cruise missiles.