BANGKOK, AUG. 31 -- In a major breakthrough in Cambodian peace talks, the Vietnam-backed government in Phnom Penh said today that it is ready to accept as a basis for discussion a U.N. proposal already approved by the guerrilla resistance.

The announcement capped four days of progress in efforts to settle the 11-year-old civil war. On Tuesday, the United States and the four other permanent members of the U.N. Security Council proposed that Cambodia be ruled by an interim government supervised by the United Nations until free elections can be held. The interim administration would oversee five key Cambodian ministries during the transition.

In New York, U.S. officials tried today to win Vietnam's approval of the U.N. plan. However, Vietnam was noncommittal.

Today, a Cambodian official said his government "accepts a major role played by the United Nations during the transitional period, notably the right to organize free and fair elections."

"I think that it {the U.N. plan} could constitute a basis for the discussions among the Cambodian parties," said Hor Nam Hong, the deputy prime minister in charge of foreign affairs, in remarks carried by the official Cambodian news agency and monitored in Bangkok.

The Phnom Penh Communist regime is battling a guerrilla coalition composed of the Communist Khmer Rouge and two non-Communist groups. The United States has supported the two non-Communist groups and China has armed the Khmer Rouge.

When Vietnam invaded Cambodia in late 1978, it ended a nearly four-year Khmer Rouge reign in which over a million people are thought to have died by execution or in slave labor camps.

Hor Nam Hong said his government was ready for peace talks anywhere, anytime. He said talks were to take place soon in Jakarta, Indonesia. Indonesian Foreign Minister Ali Alatas said today in Jakarta that the meeting should take place in early September.

Hor Nam Hong said his government agreed that "certain important ministries" could be temporarily supervised by the United Nations.

The Security Council plan covers governing Cambodia during the pre-election period, a temporary military setup, elections under U.N. auspices, human rights protection, and international guarantees that Cambodia will be nonaligned and democratic.