Interim U.N. Rule Considered for Cambodia : Southeast Asia: Five Security Council members meet in Paris. China reportedly has softened its position on support for the rebel Khmer Rouge.

The five permanent members of the U.N. Security Council, alarmed by reports of battlefield advances by Khmer Rouge rebel forces in Cambodia, met here Monday to consider an Australian peace plan that calls for an interim U.N. administration in Cambodia until elections can be held.

Four of the delegates--the U.S., Soviet, British and French--reportedly went into the closed talks encouraged by a report that the fifth, China, has softened its stand regarding the Communist Khmer Rouge.

China is regarded as the key to the success of any peace plan because it is the Khmer Rouge’s main arms supplier. And until now, China has shown little inclination to end its support for the Khmer Rouge.

Last Friday, Igor Rogachev, the deputy Soviet foreign minister, reported that the Soviet Union and China had agreed in bilateral talks that the United Nations should play a “very major role” in any peace settlement in Cambodia.

Under the Australian proposal, the Cambodian seat in the United Nations, now held by a rebel alliance of three factions that includes the Khmer Rouge, would be left open pending elections. In the interim, Cambodia would be governed by U.N. bureaucrats with the help of Cambodian civil servants.

A 19-nation peace conference here in August broke down over the Khmer Rouge question, and recent military advances by the Khmer Rouge have raised fears of a return to power by the notorious Khmer Rouge leader Pol Pot.

In light of the reported Khmer Rouge military advances, the Western members of the Security Council appear increasingly unwilling to support even a token political role for the Khmer Rouge, which ruled Cambodia between 1975-1978 and is believed to have killed up to a million Cambodians.

French President Francois Mitterrand said in a speech last week that “no compromise is acceptable with the Khmer Rouge.” Going into Monday’s talks, the French foreign minister, Roland Dumas, said the main purpose is “to seek, by all means possible, a solution to the conflict preventing the return to power of the Khmer Rouge.”

If the five permanent members of the Security Council can agree on the Australian plan, it would pave the way for a renewal of international peace talks scheduled tentatively for next month in Indonesia.

In the abortive peace talks here in August, the Western powers went along with a proposal by Prince Norodom Sihanouk, head of one of the rebel factions, that the Khmer Rouge be allowed to participate in an interim government. Sihanouk argued that without the participation of the Khmer Rouge, the most powerful of the rebel elements, no peaceful transition would be possible.

But in the face of intense international opposition to the Khmer Rouge, the Western countries appear to be backing away from Sihanouk. There appears to be increasing recognition that the non-Khmer Rouge leader with the best chance of ruling Cambodia may be Prime Minister Hun Sen.

Although Hun Sen, 38, was installed by invading Vietnamese forces in 1979, he has since won the respect of some regional powers, including Australia, for the flexibility of his leadership after the withdrawal of Vietnamese troops last summer.

Agence France-Presse, the French news agency, said Sunday that the Hun Sen government has recently developed a peace proposal that would allow portions of the country to be governed by rebel forces in the territories they now hold.