Many countries, including the United States, want Vietnam to end its occupation of Cambodia and send its 100,000 troops home. Vietnam itself wants to go home. The question that is holding everything up is simply this: What would be left behind?

The fear is that the Khmer Rouge - one of three guerrilla factions fighting the Vietnamese occupation - could gain control in the vacuum left after a Vietnamese withdrawal.The Khmer Rouge radicals seized Cambodia in 1975 and for three years carried out a fanatical program of ideological "purification" that amounted to genocide. In the killing fields of Cambodia, some two innocent million people died, a significant part of the entire population.

Vietnam invaded in 1978 and fought a successful campaign against the Khmer Rouge, occupying much of the country. Other Cambodian resistance forces gradually arose - some of them non-communist - and joined the battle. None have had great success, but the war drags on.

A chance to end the struggle will take place Monday when the rebel groups and Vietnam meet in Indonesia to discuss a possible peace. However, if a peace pact leaves the Khmer Rouge in control again, the future looks grim for the long-suffering people of Cambodia.

The U.S. is not a participant in these talks, but it should bring what influence it can to bear on China, which backs the Khmer Rouge as part of its anti-Russian policy. The Soviets back Vietnam.

If China will end its support of the Khmer Rouge, and if Thailand will close its borders and refugee camps to that murderous band, then other insurgents can take charge and perhaps restore former ruler Norodom Sihanouk to power. China could agree because, peculiarly enough, Sihanouk is a Chinese client as well, although he opposes the Khmer Rouge.

Bringing about a Vietnamese withdrawal without bringing back the Khmer Rouge is in everyone's interest - especially the Cambodian people.