By Gershom Gorenberg

JERUSALEM — A sewage reservoir in the northern Gaza Strip was in danger of bursting, my morning paper reported last week. The sewage couldn't be pumped to new filtration ponds because of power shortages caused by Israeli restrictions on fuel supplies to the Hamas-ruled territory. If heavy rain — or a stray rocket — cracked the reservoir's earthen sides, a flood of filth would threaten lives and poison the surrounding land. The Haaretz reporter got the story by phone. For security reasons, Israel doesn't let its journalists enter Gaza.

Today, that story seems like a memory from another age, when one could still worry about merely potential disasters. Since then, a different kind of dam has collapsed completely, one that held back fury and fire. As I write, the death toll in Gaza from Israeli bombardment has topped 300. Palestinian rocket fire, intended indiscriminately for civilians, is reaching wider areas of Israel than in the past. Rumors say a ground invasion of Gaza is near. Friends whose sons have received reserve call-ups talk in worried whispers.

Yet that week-old report from Gaza is a clue to how we reached the current crisis. It hints, obliquely, at the blind trust that leaders on both sides put in force, and at their inability to imagine correctly how their enemies will respond to their actions.

Israelis see little of life in Gaza. A story on a dangerously weak reservoir was a rare and fragmentary glimpse. Israeli journalists can report on the far side of the Earth more easily than on that slice of territory 40 miles from Tel Aviv. Besides that, each side in a conflict is concerned with its own suffering. The other's pain is at the very edge of peripheral vision.

During the six-month "calm," or cease-fire, between Israel and Hamas, we knew that rockets were still being fired sporadically from Gaza into southern Israel, violating the agreement. Yet for Gazans, what mattered was that they continued to live under siege conditions, with the supply of goods into the territory tightly controlled. As far as Hamas was concerned, Israel's clampdown on Gaza's borders was also breaking the deal. Because the cease-fire was based on unwritten "understandings," which each side understood differently, it's difficult to judge that claim.

After six months — on Dec. 19 — Hamas declared that the cease-fire had expired. It concluded that Israelis understood force only. With intensive rocket fire, the organization's leaders apparently believed, they would push Israel to agree to improved conditions — lifting the blockade, extending the cease-fire to the West Bank.

For angry people, force is seductive. It would have taken only a few moments of thought to predict that no Israeli politician would want to show weakness, to lift the siege because of rockets hitting Israeli towns — especially a few weeks before an election.

Instead, the triumvirate of Israeli leaders — Prime Minister Ehud Olmert, Foreign Minister Tzipi Livni and Defense Minister Ehud Barak — decided to unleash the air campaign against Gaza, in all likelihood to be followed by a ground offensive. Our leaders, it seems, also have been seduced by force. At the least, they expect that the onslaught will persuade Hamas to stop attacks against Israel. More likely, they have the same hopes for the military campaign as they had for the siege: that it will turn the Palestinians of Gaza against Hamas. Again, a brief effort to assume the other side's perspective leads to the opposite conclusion: Palestinians — in Gaza and in the West Bank — will blame Israel, not Hamas, for the bloodshed.

It is possible that Israel's attacks on government institutions, including the police, will weaken Hamas' control or even shatter the regime in Gaza. But will that benefit Israel? The most likely result will be chaos, a version of Somalia on our border. There will be no one to stop factions that are even more radical than Hamas from firing rockets. If Israel's army reoccupies Gaza, it will be the target of a new guerrilla campaign. Three months from now, we may long for the control that Hamas exerted. Our leaders are right that a country must defend itself. But while choosing a military option, they've failed to persuasively define limited, achievable goals.

Before they chose blunt instruments, each side had better choices. In November, Egypt proposed a compromise to end the Palestinian political split between Hamas and Fatah, Gaza and the West Bank. The deal would have created a coalition government under Palestinian President (and Fatah leader) Mahmoud Abbas, Israel's chosen negotiating partner, for several months before new elections in both parts of Palestinian territory. With Gaza part of Abbas' fiefdom, Israel politically would have had a harder time maintaining the blockade. But Hamas rejected the deal, apparently because of internal divisions.

Israel had mirror-image options while the cease-fire, however shaky, was in place. It could have passed the message that it was willing to recognize a Palestinian unity government and end the siege. Hamas would have faced domestic pressure to moderate its positions and work with Abbas.

Instead, our leaders kept hoping that the siege would provoke an uprising against Hamas.

Now the diplomatic choices are much more difficult. Captured by fury, afraid most of all of appearing weak and inviting worse aggression, each side is unable to back off. The flood has been released.

Gershom Gorenberg is the author of "The Accidental Empire: Israel and the Birth of the Settlements, 1967-1977" (Times Books). He blogs at southjerusalem.com.