NATO leaders in Lithuania for this week’s annual summit will cheer their growing cooperation since the Ukraine war began, but the key question is whether they can commit to ensuring Kyiv’s victory.

Not just its survival, but battlefield blows powerful enough to force Vladimir Putin to stand down — and, at a minimum, leave Ukraine in a strong position for peace negotiations.

That is: No “end” to the war that merely lets Putin rebuild for another invasion.

NATO support is particularly crucial now, as Ukrainian forces push their counteroffensive against entrenched Russian troops.

The alliance is gradually doing better on that front, upping the quality and quantity of weapons it’s sending Kyiv.

But too gradually: Ukraine still needs more advanced equipment and a sped-up delivery schedule to succeed.

Only last week did President Joe Biden agree to send cluster munitions, most of a year after Kyiv first requested them.

The delay’s unforgivable: Russia’s used them freely on Ukraine.

(Behind the holdup is Western elites’ qualms because unexploded munitions pose a threat to civilians post-conflict. But the obvious answer has always been for Kyiv and its Western European supporters to commit to a postwar cleanup of every site — not risking defeat for the sake of misplaced humanitarianism.)

The war has certainly woken Europe up: Most nations are boosting defense outlays, and 11 of NATO’s 30 members this year should at least meet the alliance’s minimum target of spending 2% of GDP on their militaries, up from just three in 2014.

The alliance has also expanded, with Finland joining in April (doubling NATO’s Russian border and complicating any new Kremlin plans for aggression to the west) and Sweden’s entry is likely soon.

And it’s clearly time to start planning on admitting Ukraine once this war is over. It’s the best way to ensure Russia doesn’t re-invade, and so guarantee the war stays over.

Such a NATO commitment will also make it politically possible for Ukraine to agree to a peace deal that inevitably will fall short of hardliners’ hopes.

Yes, the war must end before Ukraine can join, otherwise all NATO nations would be instantly obliged to enter the conflict.

Yet once the fighting is over, Ukraine’s membership should be a no-brainer.

NATO deterrence prevented Soviet aggression in Western Europe for nearly half a century; a strengthened alliance can produce the same results now with Russia.