By Jonathan Marcus
Diplomatic Correspondent, BBC News
A knockout blow against Hamas could require the re-occupation of all of Gaza
For all the chaos and bloodshed in the Gaza Strip, this is not Israel's final reckoning with Hamas.
It is instead by far the bloodiest battle in a sporadic, but increasingly bitter war between Israel and the Islamist Palestinian group that has controlled the Gaza Strip since June 2007.
There will be future rounds, future battles, and for this reason how this latest upsurge in violence ends matters to both sides.
Both Israel and Hamas are sending out clear messages. From Hamas it is one of defiance. They will not yield to Israel's superior force. And the rocket fire into southern Israel will continue.
Israel is signalling that this operation could go on for some time; the mobilisation of reserve soldiers and the massing of armoured and mechanised units on the border with the Gaza Strip indicates that this could turn into a ground war as well.
However the number of reservists called up - some 6,000 to 7,000 - would be insufficient for a knockout blow against Hamas, which would require nothing less than the re-occupation of the whole Gaza Strip.
Some limited ground operations may be launched. But the aim will be the same as that of the air attacks - to force Hamas to halt the rocket fire and re-establish some form of truce.
Such a truce is in the interests of both sides. The Israeli government needs to halt the rocket fire into southern Israel. Yes, a general election is looming, but this is not really or simply a matter of electoral necessity.
Palestinian rocket fire can now extend some 30 to 40km into Israel, bringing a significant swathe of the country into range, including Beersheba and the port city of Ashdod.
Israel's casualties have been low; very low in contrast to those of the Palestinians. But seen from the Israeli perspective that is not the point; the threat of Palestinian missile fire is making it impossible to lead a normal life in a large part of the country. The popular pressure for action has been growing ever stronger.
A truce would suit Hamas as well. It remains relatively isolated in the Arab world.
It needs to re-build and re-secure its hold on power. It wants to get the crossing points into the Gaza Strip open on a much more regular basis in order to show that it can deliver economic benefits to the Palestinian population as well as waging the military struggle against Israel.
What prompted this upsurge in fighting was, paradoxically, a battle to determine the conditions of a new truce. Hamas has been very unhappy with the way things worked last time.
Rocket fire into Israel did subside considerably. But the crossings only opened sporadically. In practical terms, Israel's economic blockade got ever tighter.
If any new interim truce or arrangement is to survive, then it will have to deal with Israel's very real security concerns. But it will also have to encompass a totally different regime in terms of the border crossing points
No wonder, then, that many Palestinians saw Israel's withdrawal from the Gaza Strip in 2005 as largely irrelevant. Israel still controls the Gaza Strip's air-space and its maritime approaches, along with nearly all of the land crossings into the territory.
Palestinians see themselves as locked up in a vast prison, with the population at large paying the price for the enmity between Israel and Hamas.
Of course, there is one other important land crossing - between the Gaza Strip and Egypt. But this, too, has largely remained closed. Egypt is fearful that the Islamist militancy of Hamas will bolster similar groupings inside Egypt.
Hamas also objected to the Israeli army's determination to attack any of its fighters approaching the border fence with Israel. Israel sees this as legitimate self-defence; a way of preventing bombings or kidnap attempts against its soldiers.
So as the truce neared its end Palestinian rocket fire picked up; as did Israeli responses. Hamas sought gradually to escalate matters by its choice of targets and the range of its missiles, hoping to set a new status quo on its terms.
Israel had clearly foreseen this possibility and was having none of it. It was determined to set the rules of the game and thus launched its air onslaught against Hamas on Saturday. The aim - to force Hamas to back down.
So, the fundamental question now is whether this goal is achievable. It's a matter of time as well as military force. The longer the onslaught continues, the greater the international pressure will be for Israel to halt its operations.
There is ample evidence that force alone cannot halt the rockets. A major Israeli ground incursion into the Gaza Strip in early 2008 was hailed as a relative success, but it never managed to stop the missile fire completely. The six-month long truce - brokered by Egypt - followed on in the wake of this operation.
Israeli leaders seem to have deliberated carefully ahead of this operation - a marked contrast to the way the Olmert government rushed into the war with Hezbollah in Lebanon in the summer of 2006.
But many Israeli commentators are asking if one of the main lessons of that war has really been learnt; does the Israeli leadership, having embarked upon military action, know when to stop?
Halting the fighting will involve some diplomatic spade-work drawing in a number of external actors - Egypt certainly, probably the United States and maybe even Turkey as well. It is unlikely to be tidy. Hamas will want to save face. It will not capitulate.
Much depends upon the organisation's complex internal politics, with divisions between the military and political leadership inside the Gaza Strip and between the leaders in Gaza and those residing in Syria.
This battle will end. But it will only set the scene for future engagements. Meanwhile, the situation for the population of the Gaza Strip becomes ever more precarious.
If any new interim truce or arrangement is to survive, then it will have to deal with Israel's very real security concerns.
But it will also have to encompass a totally different regime in terms of the border crossing points; one that will allow some real economic opportunity and stability for Palestinians in the Gaza Strip.