TEL AVIV — Suppose Israel manages to prevent its campaign in Gaza from turning into a repeat of its disastrous war against Hezbollah in Lebanon in 2006. Suppose the army does not get bogged down fighting in the narrow streets of Gaza's refugee camps and international outrage at the spiraling death toll does not force it to pull out with rockets still falling on Israeli towns. Suppose no soldiers are taken hostage and Hamas suffers enough damage to force it to accept a cease-fire on Israel's terms. Then what?

Israeli leaders say often that the result will be to "re-establish deterrence" against Hamas, and by extension against Hezbollah and others. This harks back to the glory days when Israel defeated three Arab armies in 1967 and fought off surprise attacks from Egypt and Syria in 1973. The trouble is that "deterrence" does not exist.

The effect of deterring conventional military attacks, as Israel did back then, was that aggression found other channels. For more than three decades, the main threat to Israel has been not from conventional armies but from guerrilla movements like Hamas and Hezbollah. And these groups cannot be deterred.

During the 2006 war, the Hezbollah leader, Hassan Nasrallah, said that merely surviving an Israeli onslaught would equal victory for his movement. The same is true of Hamas — even more so, in fact, since it is the only real power in Gaza, whereas Hezbollah is in finely balanced competition with other Lebanese parties. (Indeed, though some Israelis say that Hezbollah's current silence is proof that deterrence works; the real reason it has not intervened on behalf of Hamas is probably that it does not want to upset the political balance just ahead of the Lebanese elections a few months away.) Deterrence has to be equal to the enemy's fear of defeat; when the only defeat is annihilation, there is no deterrence unless Israel is prepared to reduce all of Gaza to rubble.

Even if Israel now manages to impose a cease-fire on its terms, the calm will be short-lived unless it is willing to reoccupy much of the Gaza Strip indefinitely. Moreover, as long as Israel plays the role of aggressor in Palestinian eyes, Hamas' support remains high. And each attack has weakened the relative moderates within Hamas and strengthened its most extremist leaders.

Israel needs instead to abandon its military concept of deterrence in favor of a more pragmatic political one. What could deter Hamas is the fear that by using violence it will lose support among its people.

How to create this? It is worth remembering that Israel launched its operation after the breakdown of a cease-fire that had held, reasonably well, for several months. Each side accused the other of breaching it, both with some justification. Instead of trying to re-establish the cease-fire, Israel's leaders, driven by the need to bolster their ratings ahead of an election in February, decided to try to strike a decisive blow against Hamas.

What Israel should do now is work for a cease-fire on terms that allow both sides to save some face. It should then do something it has done far too little of in the past: Improve Gazans' living conditions significantly. The aim should be to construct a long-lived state of calm in which Hamas has more to lose by breaching the cease-fire than by sticking to it.

In the longer term, Israel will have to accept that Hamas is no fringe movement that can be rooted out and destroyed, but a central part of Palestinian society. This will be the hard part, not least because of the opposition from Hamas' secularist Palestinian rivals, Fatah.

But even though Hamas' stated goal is Israel's destruction, it has said many times that it would accept a truce extending decades. Some former Israeli security chiefs argue that such an accommodation — a peace treaty in all but name — would eventually oblige Hamas to accept Israel's existence, or else lose its own base of support. It is a gamble, certainly. But the alternative is more innocent lives lost, more extremism and ultimately more trouble for Israel.

Gideon Lichfield, a correspondent for The Economist, was the magazine's Jerusalem bureau chief from 2005 to 2008. He wrote this commentary for The New York Times.