AT pivotal moments, the chaos surrounding the Soviet coup overshadows a Southeast Asia still wrestling with the cold war.Next week, the four warring factions of Cambodia and their international patrons prepare for a crucial new round of negotiations to end the country's 12-year civil war. Although the peace process has gained momentum in recent months, the Soviet turmoil comes as the Phnom Penh government, backed by Vietnam and the Soviet Union, and the three-party resistance, supported by China, the United States, and noncommunist countries in the region, remain at odds over a controversial United Nations peace plan. In the Philippines, the coup attempt heightened debate over extending the leases of US military bases, political analysts say. Some members of the Philippine Senate, which must ratify the treaty, say the Soviet coup will pressure the US to renegotiate the agreement which calls for $203 million in annual compensation. The current lease expires Sept. 16. But diplomats say the Soviet developments have thrust into the forefront regional concerns for a continued American presence to match Soviet naval power in the Pacific Ocean. The Soviet Union, a longtime Vietnam ally, uses the former US Air Base at Cam Ranh Bay, Vietnam, and recently slowed plans to withdraw from the Southeast Asian facility. "The cold war never really ended in Asia," says an Asian diplomat reached by telephone in Manila. "The events in Moscow have thrown into sharper focus the need for the United States at Subic Bay." While Western diplomats take a watchful stance, Asian diplomats in Bangkok predict continued progress toward a peace settlement in Cambodia despite the tumult in the Soviet Union. Pointing to Moscow's pledge to leave foreign policies intact, Soviet Ambassador-designate Oleg Bostorin in Bangkok played down the coup's impact on the Cambodian meetings. Preoccupied at home, the Soviet Union is in no position to restore cuts in military and economic aid to Phnom Penh and Vietnam, which have crippled both economies and nudged them toward settling the conflict, Western observers say. This week, Chea Sim, the powerful chairman of Cambodia's National Assembly in Phnom Penh, offered a concession which could further propel peace talks, observers say, although the official reportedly was unaware of Moscow events when doing so. In a speech, the official dropped references to "genocide" committed by the Khmer Rouge and its leader, Pol Pot, in the 1970s. The radical Marxists of the Khmer Rouge are blamed with the death of more than 1 million Cambodians by starvation and execution. However, Vietnam, whose recent rapprochement with China revived the stalled negotiations this summer, could become less accommodating and slow the talks if Communist Party hard-liners draw encouragement from the coup, a Western diplomat said. In Hanoi, an unidentified government official criticized Gorbachev in a Reuters interview and said a return to hard-line communism in the Soviet Union could mean a financial gain for Vietnam. Both Chinese and Vietnamese leaders were terrified by the communist collapse in Eastern Europe and Soviet reforms under Gorbachev. The possibility of a hard-line revival also fueled divisions in Phnom Penh between the more orthodox Communists, lead by Chea Sim, and reform-minded officials headed by Prime Minister Hun Sen. Factional infighting in the Cambodian capital poses a major threat to any peace accord, political observers say. The uncertainty comes as the Cambodian factions lead by Prince Norodom Sihanouk, the country's hereditary leader, and the five permanent members of the United Nations Security Council which are overseeing the talks, tackle touchy issues in meetings next week in the Thai resort town of Pattaya. On the table will be a controversial plan calling for the United Nations to administer Cambodia during a transition to peace and monitor elections and a cease-fire. Phnom Penh leaders have resisted proposals to dismantle their administration and disarm the factions before holding elections. "The Americans don't know what kind of administration they want," says a European diplomat. "There is no way Phnom Penh will accept the Perm Five [plan]."