UNTIL RECENTLY, the international momentum on Darfur seemed positive. The plight of Sudan's western province was recognized as the world's most pressing humanitarian crisis, and a congressional resolution described the eradication of African villages by a government-backed Arab militia as genocide. After much misguided talk about getting Sudan's government to protect civilians in the region -- a wishful idea, given that the government's proxies have taken children from mothers and tossed them into fires -- a consensus has more or less formed that foreign peacekeepers are needed. But now, despite this progress, it seems the momentum is fizzling, in which case the world will have woken up to a catastrophe and understood what it must do -- and then decided not to do it.

About 1.5 million Darfuris have been chased from their homes, some leaving behind villages whose wells have been poisoned with the dismembered bodies of their loved ones. Until they return home, they will depend largely on food airlifted at vast cost by the international community. But they are not going to return until it is safe, and that means that a trusted force must be on hand to protect them. The most extensive survey of refugees carried out so far suggests that a quarter of the attacks on civilians have been perpetrated by the government, and half of such attacks beyond that featured the government assisting the militia. The trusted force that could make refugees feel secure cannot be the government. It could, as Senate Majority Leader Bill Frist has suggested, involve fighters from the Sudan People's Liberation Army, the southern rebel army that recently negotiated peace with the government. But it is more likely to involve foreigners.

A few weeks ago, British and Australian leaders hinted that their countries might supply peacekeepers. Recently, however, no hints have been forthcoming. The best hope for intervention comes from the African Union, which already has a handful of troops in Darfur and which stands ready to provide perhaps 3,000 -- by no means enough for an area the size of France yet certainly worth having. But the African Union is unwilling to deploy troops in the face of Sudanese resistance, which for the moment is determined. It would be nice if the young organization, which has discredited itself by its failure to deal more severely with renegade members such as Zimbabwe, could muster the will to present Sudan's government with an ultimatum. But this seems unlikely.

If the African Union is unwilling to play hardball, in theory the United Nations could do so. In July the Security Council passed a resolution giving Sudan's government 30 days to ensure the safety of Darfur's civilians. But although Sudan has not complied, council members show no inclination to follow up with sanctions; instead, there is talk of another resolution, which will urge, exhort and call upon Sudan to do the right thing but which won't spell out the consequences should Sudan again fail to do so. Nor is there much prospect of pressuring Sudan via other channels. The Bush administration has depleted its diplomatic capital and is not inclined to assemble a coalition of the willing that could act if the council and the African Union prove immobile.

So the efforts on Darfur have hit a roadblock. Foreign peacekeepers are evidently necessary, but there is no mechanism to force their deployment. The risk is that, with few cards to play, outsiders will accede to a face-saving deal with Sudan's government, perhaps trading an invitation to deploy African Union forces for a mandate so restrictive as to render them useless. But the United States and its allies need to shake themselves awake. Hundreds of thousands of lives are at stake in Darfur, and it is up to the world's leaders to decide if they care.