Though peace seems distant, the United States and Europe are debating how to guarantee Ukraine’s security once the fighting with Russia stops, even without a total victory by either side. West Germany may provide a model, a precedent for admitting a divided country into NATO.

Despite its division and unhappy role as the border between nuclear armed rivals during the Cold War, West Germany became a NATO member in 1955, benefiting from the alliance’s protection, without ever giving up its commitment to unification, finally realized in 1989.

For Ukraine, much will depend on the shape of the battlefield after its coming counteroffensive, and whether the outcome leads to some kind of extended cease-fire, relatively stable borderlines, or even peace talks.

As NATO’s yearly summit approaches in July, its members are discussing what they can offer Ukraine’s president, Volodymyr Zelensky, who wants more concrete assurances that his country will join the alliance.

The West German model is gaining traction in some European capitals as a way to provide Ukraine real security, even if it does not immediately regain all its territory.

Germany is an example of NATO accepting a country with “significant and unresolved territorial issues” and a form of enemy occupation, said Angela E. Stent, an expert on Russia and Germany and author of “Putin’s World.”

“When West Germany joined NATO, there was what you could call a monumental frozen conflict,” she said. “And yet it was felt very important to anchor West Germany in the Western alliance, and so West Germany joined. The Russians complained about it and said it was very dangerous, but they were powerless to prevent it.”

After World War II, there were various options considered for what to do about occupied and divided Germany, much as there are now for Ukraine.

Soviet leaders spoke of a united but neutral Germany, on the model of Austria. However tempted, the Western powers resisted. And in fact Ukraine itself initially proposed neutrality just after the Russian invasion of February 2022.

Konrad Adenauer, the first chancellor of West Germany, chose security over territory, and Germans supported him, re-electing him until he resigned in 1963.

“Adenauer decided that it was more important to have a solid defense agreement with the West and led West Germany into NATO,” said François Heisbourg, a French defense expert. “It was a brave decision, because it meant unity wasn’t going to happen easily.”

Ukraine is of course a different case. When West Germany joined NATO, it was not at war with East Germany and both entities had been recognized as individual states in 1949, said M.E. Sarotte, author of a diplomatic history, “Not One Inch,” about the enlargement of NATO, German reunification and the Russian responses.

While West Germany’s Constitution preserved the goal of unification, “the reality on the ground was what had formerly been the occupation zones coming out of World War II had hardened into state divisions,” Ms. Sarotte said. “While no one was happy about this, you had this clear, hard border, and so that provided a clarity that doesn’t exist in Ukraine.”

Not yet, anyway. But as Charles Kupchan and Richard Haass suggest in a recent essay in Foreign Affairs, few expect the coming Ukrainian counteroffensive to drive the Russians completely out of sovereign Ukraine, including Crimea. If battle lines harden, they suggest, the United States should push for peace negotiations, even if neither Ukraine nor Russia seem eager.

That won’t be easy. Ukraine worries that a cease-fire would endorse Russian control over a significant amount of Ukraine; Russia seems to think it can outlast Western support for Ukraine. Neither side is now open to negotiations, and Mr. Zelensky, in his own peace plan, insists that Russian troops first withdraw from all Ukrainian territory.

But as suggested by the battle for Bakhmut, the city Russia claimed to have seized after almost a year of fighting, even modest shifts in the front line come at tremendous cost in lives and matériel.

Few in the West want an endless war, already fearing the decline of popular support for limitless funding and the shortfalls in manufacturing the tanks, air defenses and ammunition Ukraine needs.

There have been various proposals for making Ukraine an indigestible hedgehog for Russia, so stuffed with sophisticated Western weaponry that, even if not a member of NATO, it could deter Moscow. That is the core of an idea first proposed by a former NATO secretary-general, Anders Fogh Rasmussen, and a top Zelensky aide, Andriy Yermak.

The Rasmussen idea, which many in NATO favor for now, suggests Israel as a model, where Washington’s commitment to its ongoing security is clear even without a specific mutual-defense treaty. But the problems are clear: Israel has nuclear weapons, while Ukraine does not. And even bilateral defense commitments from NATO members for Ukraine could still end up dragging the whole alliance into a future Russia-Ukraine war.

So many officials and analysts believe, as Kaja Kallas, the prime minister of Estonia, said in a recent interview, that the only real security for Ukraine is NATO membership, “when conditions allow.”

At the alliance’s summit in Vilnius, Lithuania, in July, Ms. Kallas said, NATO must lay out a more concrete road map for Ukraine to join, reconfirming a promise first made in 2008.

“The only security guarantee for Ukraine is NATO membership,” she said, citing the protection membership affords her own small country. “We don’t have war here because we are members of NATO,” she said.

Another benefit, she said, is that having Ukraine inside NATO would be “cheaper, much cheaper” than making it a militarized hedgehog for the next 50 years.

The counterargument, held widely in Washington and Western Europe, is that NATO cannot accept a country at war over disputed territory, and that such a move could push Russia to escalate further, even with nuclear weapons, before Ukraine could enter the alliance. But so far, Russian threats of escalation have proven hollow.

For now, ahead of the summit, NATO countries are preparing a medium-term plan of pragmatic military assistance for Ukraine, including guaranteed arms supplies and further integration into NATO’s world. But Mr. Zelensky wants a political promise he can take home.

Still, if the war does not in the end produce large-scale Russian withdrawal and defeat, what could prove convincing to Mr. Zelensky and Ukrainians — giving any peace talks the most leverage — would be NATO membership, behind solidified cease-fire lines, perhaps patrolled, Mr. Heisbourg suggests, by a coalition of peacekeeping forces from NATO and other countries, like India or even China.

That would be coupled with the promise, as in Germany, that Ukraine’s complete reunification would remain a live issue for the future. NATO membership would solidify the peace and allow reconstruction, private investment and the return of many refugees.

If there is only a cease-fire, Ms. Stent said. “there’s no real resolution to this war, you don’t know when it’s going to start again.”

“But the whole point of taking Ukraine into NATO would be to make sure that Russia didn’t attack Ukraine again,” she said, “because what we’ve seen in this war is that NATO is the only form of deterrence that’s worked so far against Russia.”