BANGKOK, FEB. 6 -- Cambodia's Vietnamese-installed government has postponed parliamentary elections planned for later this year in an effort to promote a settlement of the country's 12-year-old civil war, the official SPK news agency reported today.

The agency said the government of Premier Hun Sen had put off the scheduled vote in another attempt to encourage the coalition of three rebel guerrilla factions to agree on a firm truce and to press ahead with talks on a new constitution under a U.N.-sponsored peace initiative. State radio said that if the guerrillas fail to respond, the government will hold the elections in 1992 to meet provisions of Cambodia's current constitution.

The government and the resistance coalition -- led by former Cambodian monarch Norodom Sihanouk and including the Chinese-backed Marxist Khmer Rouge -- have been engaged in slow-moving discussions to bring peace to the war-torn nation, carried on chiefly by a transitional negotiating council representating all warring parties. The U.N. proposal calls eventually for the world body to disarm the factions and oversee administration of Cambodia during preparations for free, multi-party elections.

Chea Sim, the No. 2 man after Hun Sen in the Phnom Penh government, urged the guerrillas last Saturday "to move forward to put an end to the conflict," the SPK report said. But he rejected the guerrillas' demand that the government and army be dissolved before multi-party elections take place.

Phnom Penh has argued that the resistance demand would violate the U.N. Charter and invite attacks on the government by the Khmer Rouge, the strongest of the three guerrilla factions. Hun Sen's government has agreed to let the United Nations organize the elections, regroup rival forces and armaments in garrisons and monitor ministries that could directly influence the balloting, Phnom Penh radio said.

The broadcast said Phnom Penh had shown its desire for peace by sending delegations to talks 16 times over the past three years.