AFTER the death of a third of its population during two decades of civil war, genocide, and foreign occupation, there now seems a real chance that Cambodia may begin a more promising era. On Oct. 23, the noncommunist resistance forces, the Khmer Rouge, and the Phnom Penh government signed an agreement in Paris to end the conflict and usher in a new democratic system.United Nations administrators and military peacekeepers will now have to translate the broad statements of the political agreement into a detailed plan for achieving peaceful settlement. The question this UN advance party (UNIMAC) should be asking is whether their task in Cambodia is a realistic proposition for peacekeepers. The cease-fire plan is complex. Each of the four Cambodian forces is to move from its operational bases and regroup into predesignated assembly areas or cantonments. These will be set up and manned by teams of UN monitors. Once inside, 70 percent will disarm and demobilize and the remaining 30 percent will disarm, possibly with a view to forming an integrated national army later. Before the process can begin, each faction must declare its manpower, weaponry, and logistic arrangements. Once these figures have been mutually agreed upon, an additional force, the United Nations Transitional Authority in Cambodia (UNTAC), will supervise the cantonment process. There are several reasons why this mission could fail. It is hard to imagine that the concept of "free and fair" elections in Cambodia will appeal to the isolated communist regimes of Vietnam and China. By applying indirect pressure, these neighbors may encourage what has been referred to as the Red Solution. Although a democratic process involving the cohabitation of Cambodia's two strains of communism is unthinkable, clandestine encouragement of a less-than-democratic process cannot be ruled out. Any i nterference on this scale would overwhelm UNTAC's thinly spread resources. In the operational area the proliferation of weapons is so extensive that disarmament may not be achieved by cantonment alone. Although a cease-fire has been tacitly observed since May, there are daily acts of violence, artillery dueling, ambushes, and the continued use of mines. Individuals, local gangs, and even sizable militias may challenge the peacekeepers. In the northwest border areas some will resist if their smuggling, extortion, and arms trading activities are threatened. There is no evidence that the Khmer Rouge have abandoned their capability or longstanding intention to revive the radical Maoist system which collapsed in 1978. Because of this perceived threat from one faction, each armed force has a motive to cheat on their declarations and withhold elements of their military capability from the peace process. Elements of the Cambodian police are exempted from the cantonment process to maintain order under the supervision of UNTAC. But this apparently sound arrangement may be flawed. The 100,000 militia and regular police forces range from the Russian-trained A3 force to village security wardens. The numbers are impressive, and some local militias have defeated attacks by the Khmer Rouge. But this diversely constituted force has no effective nationwide command system that would allow it to become subordinated to UNTAC or react to contingencies outside their local areas. It will be asking a great deal of the Cambodian police to maintain order in the initial stages of the disengagement. Until a modus operandi develops, they will need the support of an international force. If Cambodia turns out to be less than a "best-case scenario," the international community must be prepared to underwrite the security of the peace process. Adequate funds must be found to pay for a realistic UN response. Contingency plans will be required for a carefully prepared reserve force in Thailan d or offshore that could rush to a trouble spot and ensure the maintenance of order locally, showing that the peace process has not been abandoned. Pressure is already mounting on the UN Secretariat to respond immediately, but a swift, ad hoc UN deployment can only succeed in a best-case scenario. Cambodia is unlikely to fulfill such an optimistic assumption. To have any chance of success, the UN teams will need massive funding and time to prepare. If they are thwarted in Cambodia by a lack of mutual trust and cooperation, the peace process will have to be abandoned, for no intervention could restore it. If, however, the process is being sabotaged by local acts of violence and lawlessness which do not amount to a nationwide crisis of confidence, then efforts must be made to save it. It would be unthinkable for the UN and the nations that are the de facto guarantors of the Paris agreement to abandon Cambodia to another year zero.