Sierra Leone is once again about to dissolve in violence. This time, however, it threatens to take the United Nations with it. A rebel leader bent on undermining a peace agreement faces a poorly organized, ill-equipped peacekeeping force that has been denied the political support that is critical to its success. If members of the Security Council do not muster the will to restore order, the credibility of the world body could be irreparably damaged.

There were no illusions about the situation in Sierra Leone when foreign troops moved in to help rebuild the country. An eight-year civil war had ravaged the country. The rebel troops of Mr. Foday Sankoh had first taken up arms to fight a corrupt and incompetent regime. But as the war continued, they committed horrific atrocities, killing thousands and hacking off the limbs of hundreds of defenseless civilians. Last July, African leaders brokered a peace agreement between President Ahmad Tejan Kabbah and Mr. Sankoh. As part of the deal, the U.N. took over peacekeeping duties from a Nigerian-led West African group. Some 11,000 troops are supposed to police the agreement and complete the disarmament and demobilization of rebel groups in time for an election scheduled for next year.

If the contingent reaches full strength, it will be the U.N.'s biggest peacekeeping force. If it does not, it is sure to be the world body's biggest headache. If the governments behind the deployment are not committed to keeping and enforcing a real peace, troop strength will be irrelevant. So far, that last ugly alternative is prevailing.