Leading article: A vacuum as perilous for the region as for Israel

There is rarely an opportune time for the departure of a national leader, but the massive stroke that felled Ariel Sharon this week could scarcely have come at a more difficult moment, either for Israel or for the region. The soldier-turned-politician inspired fierce passions - for and against - over his extended career, but his absence threatens to leave a vacuum that is every bit as dangerous as it was unforeseen.

At home, Mr Sharon had broken the old mould of Israeli politics, but not yet fully forged a new one. His new party, Kadima, was a vehicle for his recently developed centrist aspirations. He believed it matched the mood of Israeli voters, but it has not had the time to progress beyond its genesis as his personal creature. Without Mr Sharon at the helm, there must be doubts whether it can survive or become the force in Israeli politics he intended. The whole of the country's domestic political scene is in flux. Israeli officials insist that the general election called by Mr Sharon for late March will proceed whatever happens. This is a good sign, the mark of a stable democracy whose structures do not depend on the survival of individual leaders. So, too, was the efficiency with which power passed to Mr Sharon's deputy, Ehud Olmert. By no means every democracy can manage such an enforced and sudden transition so smoothly.

But the future of all Israel's major parties is now in play, along with the complexion of the country's next government. The veteran moderate, Shimon Peres, and his supporters are marooned in a leaderless Kadima. Will this young party survive? Might the Labour Party, under its left-wing leader, Amir Peretz, try to recapture the centre ground? What of Benjamin Netanyahu and the right-wing Likud Party he inherited from Mr Sharon?

The uncertainty that Mr Sharon's incapacity generates reaches into every corner of Israeli politics. Even then, it is as nothing compared with the uncertainty that has been created in the region and internationally. Alongside the predictable jubilation in some Palestinian and Arab circles, there is trepidation and even fear. Mr Sharon had sworn enemies, but enemies and friends alike felt they knew where he stood.

They watched him honour his pledge to withdraw from Gaza. They knew that he wielded authority in Israel and abroad. They understood that his priority, in what was probably the twilight of his life, was the security and survival of Israel. In this respect, he was a force for at least short-term stability at a time of immense volatility across the region.

Israel's withdrawal from Gaza has exposed the weakness of the Palestinian President, Mahmoud Abbas, and the deficiencies of his administration. That Palestinian elections set for the end of January look less certain to take place, even now, than Israel's elections in March says much about the continuing instability of the Palestinian Authority. With policy-making in both Israel and the PA now effectively suspended, the peace process is at best frozen, and possibly endangered. A strong showing by Hamas in the Palestinian elections would complicate the picture further.

But it is complicated enough already. To the north of Israel, security in Lebanon has been deteriorating and the position of Bashir Assad in Syria seems shaky. The US, heavily committed to Iraq, is locked in stand-offs with Syria and Iran. And now the man whose late conversion to peace-making seemed - against all the odds - to offer hope of a lasting Middle East peace looks unlikely to return to leadership. It is his tragedy that we may never know how far he would have gone to secure a settlement. The greater tragedy would be if his departure spelt the end of the quest for peace in the region.