NOW THAT was one story, the one on Cambodia, that brought us up short. "Cambodia Thanks U.S. for Help at U.N.," the headline said. The story went on to report that "premier" Khieu Samphan -- he now outranks the more notorious Pol Pot, but they are the crowd responsible for the genocide in Cambodia -- had warmly thanked the United States for its vote to seat "democratic Kampuchea" in the U.N. General Assembly last year. The ingratiating Khieu Samphan indicated that his organization, the old Khmer Rouge, is open to further and even direct American support of a humanitarian, political or military nature.

How is it that these completely discredited and disgusting thugs, whom Jimmy Carter accurately labeled the world's greatest human rights violators in 1978, are extending a bloody hand to the president now? The answer is that by 1979, Soviet-allied Vietnam had invaded Cambodia and installed a puppet named Heng Samrin. The Chinese and the Thais, fearing Soviet pressure and Vietnamese aggression, respectively, were trying to keep the Khmer Rouge resistance alive. The United States, which strongly opposed the invasion, was drawing closer to Peking and wanted to stay close to Thailand. At the United Natons, the Soviets sponsored Heng Samrin for the Cambodian seat. The Chinese sponsored "Democratic Kampuchea." Holding its nose, the United States backed up the Chinese on the seating issue; the administration still denies recognition to either regime.

Well, the United States gets another crack at the seating question when it comes up for its annual test in the General Assembly next month. That is the time for the United States to cut itself loose from any taint of association with the Khmer Rouge. It is bad enough that the administration, pleading geopolitical cause, took a "technical" stand in 1969 from which the Khmer Rouge has drawn comfort. Here would be some political debits now in sliding off that stand, but that is what should be done. Geopolitically, it has brought the United States no evident gains. Politically, it has been used by Nanoi to justify both its support of Heng Samrin and its suspicion of U.N. relief efforts. Morally, it is beyond characterization.

This does not mean that the United States should vote to seat Heng Samrin. He may not be the proven butcher that Pol Pot is, but, being strictly the tool of invaders, he has no higher claim to legitimacy and popular acceptance. The procedure gets complicated on credentials votes, but surely American diplomats can avoid identifying the United States with either of those Cambodian regimes. That leaves open the question of who rightfully represents the Cambodian people. It is a central part of Cambodia's continuing tragedy that, at this moment, no one has been able to establish a fair claim.