THE path toward peace in Cambodia winds through a jungle of distrust and fear where entangling vines, once cut away, seem to reappear almost immediately. Thus, shortly after the recent announcement of a breakthrough on a plan to disarm the country's factions, new problems appeared. Even so, negotiations are moving slowly ahead.The momentum comes both from within Cambodia and from outside. The four Cambodian parties to any agreement - the current communist government in Phnom Penh, the radically Marxist Khmer Rouge, and groups headed by Prince Norodom Sihanouk and former Prime Minister Son Sann - appear ready for compromise. Just as important, the outside powers whose aid has kept the civil war going want the conflict to end. China, preoccupied with its own frictions, is nudging its client, the Khmer Rouge, toward the United Nations Security Council peace plan it helped formulate last year. Vietnam, which set up the Phnom Penh regime after defeating the Khmer Rouge in 1979 and had a large number of troops in the country until 1989, is also intent on ending the conflict. Vietnam wants normalization of relations with the West, especially since the Soviet Union - its major benefactor and Phnom Penh's, too - has dropped out of the aid picture altogether. A persistent question is whether the Khmer Rouge, with its record of murderous oppression, should have any role in Cambodia's future. Is the Khmer Rouge just biding its time until it can seize power politically from within? The UN presence envisioned in the peace plan will have to be strong to prevent distortion of whatever electoral system is eventually instituted. Beyond that, economic development and an understanding of democratic procedures need to reach the villages where most Cambodians live, and where the Khmer Rouge hopes to secure its political base.