Leading article: Sunnis can only lose by rejecting this constitution

The signing of a draft constitution for Iraq, beginning with the evocative phrase "We, the sons of Mesopotamia", marks a milestone in the country's post-conflict history, even though the vast gap that exists between the high-blown phrases on paper and the grim reality on the ground is all too evident. But that the numerically dominant Shias and Kurds have reached an accord on most of the main points concerning the future governance of their country is in itself an achievement, and will be hailed in Washington and London as a sign that their much-touted "exit strategy" is finally working.

The black cloud on the horizon remains the continuing opposition of the Sunnis, or at least their leaders, to any document that appears to enshrine federalism. To their mind this threatens Iraq's unity as a state and consequently their access to a share of the wealth from the country's oil fields, which lie in the Shia and Kurdish areas. Thus far an agreement on the federal question has proved beyond everyone's powers, and yesterday's signing ceremony was only possible after it was decided to put the federal question on hold for six months. The exact shape and competences of the regions will be left to a future parliament to decide.

With no substantive agreement in sight on the federal issue, Sunni leaders will be tempted to campaign hard for a '"no" vote on the constitution ahead of the nationwide referendum planned for mid-October. They hold a trump card, in that a two-thirds "no" vote in three or more of the country's 18 provinces will render the entire project null and void and send everyone hurrying back to their drawing boards. As the Sunnis dominate at least four provinces, there is a strong possibility that this will be the outcome.

The desire among the dethroned Sunnis to humble both the newly ascendant Shias and the Americans, who desperately seek a deal on a constitution, will be a strong one. Whether the Sunnis would be wise in taking this path is another question. They have experienced a sharp decline in their collective fortunes since the US-led invasion of May 2003. From being the effective rulers of Iraq under Saddam Hussein and his predecessors, they have suddenly been told to adjust to the role of a fairly small minority routinely outmanoeuvred and outvoted by the tacit alliance between Shias in the south and Kurds in the north.

Their bitterness is comprehensible. Now they face the extra gall of being governed by a constitution into which they had precious little input. But the fact is that obstructionism will not restore them to the palmy position they once held. The plain and unalterable demographic reality of Iraq is that Shias make up an absolute majority of the population, while Sunnis comprise less than a quarter.

The other equally disagreeable fact of life for the Sunnis is that the regions they dominate lie outside the wealth-producing oil zone. Tempting as it might appear to bring Iraq to a total standstill over the constitution, the likely result would be an all-out civil war that Sunnis cannot win, and which would leave them in charge of a rump state shorn of natural resources.

A deal that offers Shias and Kurds the wide-ranging autonomy they seek, and which also safeguards the unity of Iraq as a state, is probably the best the Sunnis can hope for in the long term. This at least would guarantee them some share of the country's oil wealth. The question is whether - in the heat of the moment and with issues of pride at stake - this embittered community can be persuaded to see where its true interests lie.