If the United Nations has met these realistic goals by New Year's Eve, it will be a good beginning, a sign of seriousness.

The signals out of Khartoum are mixed. The United Nations has informed U.S. officials that it is already getting resistance from the regime on logistical issues. If the Sudanese continue to play these games, as they have done before, there will need to be penalties.

The United States has immediate responsibilities as well -- to provide airlift support through NATO, training for command staff, communications and computer equipment, and generators. America is obligated to pay 27 percent of the cost of the peacekeeping force, which will probably require a supplemental funding bill from Congress in 2008.

But the implementation of this resolution is, above all, a test for the United Nations. In dealing with Darfur, U.N. officials are determined to learn from past mistakes. The problem is choosing which mistake to learn from.

U.N. military planners want to avoid the debacle of Somalia that began in 1992, when peacekeepers entered a chaotic situation piecemeal and eventually left in defeat and failure. So in Darfur they want the U.N. intervention to be large and decisive -- a "big bang" -- even if that means the timeline is delayed. During a genocide, however, patience and delay have casualties.

Another U.N. failure is worth recalling and avoiding: Rwanda in 1994. While waiting for perfect circumstances to intervene, the world did little and now lives haunted by a million ghosts.

No historical analogy is exact. But the Darfur genocide is closer to Rwanda than Somalia. It requires the urgent establishment of security first.

For all the Americans who have worked and prayed for Sudan over the years, for all the churches and synagogues with banners that call us to conscience, the time to push has arrived. There are many complex steps of negotiation and reconciliation between government and rebels down the road. But we should begin with one step: 5,000 new police and troops in Darfur by the end of this year.