United Nations, N.Y. — Three years ago Prince Norodom Sihanouk had vowed never to link up with the Khmer Rouge, who were responsible for murdering tens of thousands of Kampucheans (Cambodians), including dozens of members of his own family.
Until a year ago he resisted strong Chinese pressures to form a coalition with the Khmer Rouge to help refurbish their image.
Today he is head of a coalition government formed last June that includes the leader of the Khmer Rouge, Khieu Samphan, formerly Pol Pot's second in command. Also part of the coalition is Sihanouk's former prime minister, Son Sann, now head of the National Liberation Front of the Khmer People.
Over the years, Sihanouk (here to address the United Nations General Assembly) has lost none of his flamboyance and pugnacity. Highly emotional, fiercely nationalistic, politically astute, Prince Sihanouk agreed to tell the Monitor about his hopes regarding the future of his country and to explain his strategy.
To explain his abrupt turnabout Sihanouk says that ''the situation in Kampuchea has taken a dramatic turn.''
''In terms of humanity,'' he goes on, ''the Vietnamese occupants were certainly kinder to my people than the Khmer Rouge would have been. But now, gradually, the Vietnamese are colonizing Kampuchea, taking over its riches. Little by little, Kampuchea is becoming a Vietnamese province and my people are in danger of losing their very identity.
''The same Kampucheans, intellectuals, cadres, middle-class people, who previously had urged me never to associate with the Khmer Rouge, have recently urged me to form a coalition with all the resistance groups. Fighting the Vietnamese must be given priority over all other considerations, they say. Thus I had to overcome my personal feelings in the interest of my country.''
Sihanouk does not worry what the Khmer Rouge would do once in power. ''The Vietnamese are not about to be defeated by our guerrilla forces, nor are they likely to allow the pro-Chinese Khmer Rouge to take control of Kampuchea.''
In Sihanouk's view, then, the Khmer Rouge, who do most of the fighting against the Vietnamese right now, can be used as a means of pressure, a way of hurting Vietnam until, hopefully, it settles for a compromise.
A negotiated solution, in Sihanouk's view, must be worked out at a UN-sponsored conference and must lead to:
* A neutral and independent Kampuchea guaranteed by the superpowers.
* A disarmed Kampuchea (to avoid a new bloody civil war between pro-Soviet and pro-Chinese communist factions).
* Free elections, under UN supervision.
Sihanouk is not optimistic with regard to the near future. A thaw in Kampuchea will only happen, he feels, after a thaw between the Soviet Union and China has taken place. And, according to him, this is not in the cards for the foreseeable future:
''As long as China and the Soviet Union see each other as rivals and adversaries, they will fight each other in Southeast Asia through Kampuchean and Vietnamese proxies.''
In Sihanouk's view the United States lacks a purposeful, dynamic policy in Southeast Asia. It contents itself with leaving the field to China and to the ASEAN countries. He says he and his 5,000 freedom fighters are getting arms from China, humanitarian aid from three Western countries, but absolutely no assistance from the US. On Oct. 6 Sihanouk is due to meet Secretary of State George Shultz and will try to persuade him to play a more active role in the region.
''I could have 30,000 men under my command if I were given adequate assistance,'' he says. As for Vietnam's peace offensive aimed at the ASEAN countries, and its offer to hold a conference to deal with ''Indochina's problems,'' Sihanouk sees it as an attempt by Hanoi to skirt the Kampuchean issue.
Sihanouk admits that there is no great love between himself, Son Sann, and Khieu Samphan. ''Same bed, different dreams,'' he says, quoting the Chinese proverb.
The populist, progressive-minded monarch dreams of an independent, peaceful, neutral, social democratic Kampuchea. He is hated by the Kampuchea upper middle class headed by conservative Son Sann, which is republican. And the Khmer Rouge have but contempt for both Sihanouk and Son Sann - ''two bourgeois puppets.'' Their strategy appears simply to last as a fighting force, and hope that Vietnam will ultimately fall under Peking's influence. They would then be China's instrument for controlling Kampuchea.