THE GREATEST humanitarian catastrophe since the Rwandan genocide is at last getting the attention it deserves. Over the past two days Secretary of State Colin L. Powell and U.N. Secretary General Kofi Annan have paid visits to Darfur, the western Sudanese province where more than 1 million people have been chased out of their homes by government-backed militia forces, and where the death count in unsanitary and undersupplied refugee camps is likely to exceed a third of a million. Mr. Powell and Mr. Annan aimed to impress on Sudan's government that inaction in the face of this suffering will not be tolerated, and the pressure appears to be working. Having deliberately created this crisis, Sudan's rulers now promise to rein in their militia allies; to stop impeding humanitarian access to Darfur; and to open political talks today with Darfur's rebels, whose uprising provoked the monstrous policy of burning villages, turning farmers into refugees and waiting for them to die.

The first challenge over the coming weeks will be to hold Sudan to these commitments. Given the space to do so, the government will doubtless revert to its pretense that the plight of Darfur is exaggerated. There is "no famine," the foreign minister declared on Tuesday, notwithstanding reports from aid workers that famine-related deaths are running at about 1,000 per week. Equally, a government that oozes contempt for the lives of its own citizens cannot be trusted to rein in their assailants. When students in Sudan's capital tried to deliver a petition this week to Mr. Annan about the plight of Darfur, security forces opened fire on them. To ensure that Sudan sticks to its commitments, the United States and its allies must push ahead with a U.N. Security Council resolution that threatens members of the Sudanese regime with sanctions if the commitments are not met.

The second challenge is to seize the opportunity to get relief supplies into Darfur. Torrential rains are starting to make roads impassable, so this will require a major airlift as well as procurement of relief supplies on a large scale. The United Nations has appealed for $350 million to finance a relief effort, and yesterday a World Health Organization official, newly returned from the region, said it would take a fleet of 20 helicopters to contain outbreaks of cholera and dysentery in the 137 refugee camps spread out across Darfur, an area the size of France. But donor governments have come up with less than half of the money that is needed. According to a U.N. count of firm commitments since March, the United States has promised $62 million, Britain about $11 million. But Germany, France and Japan have each promised less than $4 million.

The tightfistedness of these allies is outrageous, as is the reluctance of France and other members of the U.N. Security Council to support a tough resolution on Darfur. To excuse their failure to contribute to Iraq's reconstruction, these nations complain that the Bush administration's Iraq policy was insufficiently deferential to the United Nations. But none other than the U.N. secretary general has just visited Darfur to demonstrate the urgency of humanitarian action. What excuse can there be now?