When President Bush announced his plan for a Middle East peace conference he did not stint on detail or ambition. The negotiations launched at the conference must, he said, “ensure that Israel is secure”. They must guarantee “that a Palestin-ian state is viable and contiguous”. And they could lead to “a permanent end to the conflict, and an agreement on all issues including refugees and Jerusalem”. That was in July. Since then, the key question about the conference became not whether it could lead to peace, but whether it would happen. That more than 40 countries are represented today in Maryland, among them Saudi Arabia and Syria, is itself a major achievement. It means that expectations can be raised again, if only imperceptibly. The true measure of success in Annapolis will be whether Israel and the Palestinians can agree to keep talking.

Their agenda today will, at the very least, remind them of their goal: the third of three 90-minute plenary sessions will be devoted to discussing “comprehensive peace”. But the obstacles to achieving this remain formidable. The Palestinian Authority would have to neuter a Hamas over which it lacks meaningful control, and to retain the loyalty of moderate Palestin-ians while offering an historic compromise on the “right of return” to which some have clung for 60 years. Israel would have to contemplate significant concessions in the West Bank, and both sides would have to entertain radical new visions for the governance of Jerusalem.

No one expects breakthroughs on such core issues this week, but a “final settlement” that would address them is explicitly the goal of the peace process that Mr Bush hopes to relaunch. That process faces two immediate threats. There is, first, a risk of major Arab states withdrawing their support over Israel's refusal to agree in advance of the conference on a timetable for dismantling settlements on the West Bank. This was never a realistic demand. Israel's withdrawal from Gaza has hardly yielded the security dividend for which Ariel Sharon hoped, and it would be folly now for Mahmoud Abbas, the Palestin-ian President, or the Arab League, to expect Ehud Olmert to offer further withdrawals on the mere promise of security. Israel's security, as Mr Bush has said, is non-negotiable.

The second threat to a renewed peace process is Hamas. As a pariah organisation, still committed in principle to the destruction of Israel, it is not represented in Annapolis. Yet its control of Gaza severely weakens Mr Abbas. A major purpose of this conference is to empower the Palestinian leader and further isolate Hamas. He cannot, therefore, fly home empty-handed, and the next 24 hours may prove crucial in ensuring that he does not. The concessions that Mr Abbas might reasonably seek at this stage are not territorial, but economic; specifically, a commitment in principle from Israel to ease some of the restrictions imposed on Palestinian economic activity on the West Bank by Israeli settlements and the infrastructure connecting them.

Even a tentative agreement along these lines would give grounds to hope for more substantial progress during Mr Bush's remaining 14 months in office. The Arab League is, for now, committed to the search for peace. Mr Olmert is realistic about Israel's need to develop in Galilee and the Negev rather than the West Bank. And Mr Bush himself has made clear that both sides must make major concessions as the price for peace. They are a price worth paying.