THE NEWEST BURDEN being put upon the people of Cambodia, who may have suffered more than any other group of human beings since World War 11, is different form the others. The new burden is the prosect of famine, and the difference is that some part of it can conceivably be averted if the outside world cares.

Now, throughout Cambodia the situation remains severe as a result of the upheavals culminating in the mass forced march to the countryside ordered by the Pol Pot government after its victory in 1975. Within the areas controlled by the Hanoi-sponsored regime of Heng Samrin, which displaced Pol Pot in January, the Soviets and some of the international agencies are filling what food needs outsiders are in a position to fill. It is in other areas, where the forces of Pol Pot and Heng Samrin are still fighting or in on man's land, that a condition of special urgency has arisen. The war's disruption of people and planting has driven tens of thousands of hungry Cambodians into nighboring Thailand.The Thais, feeling overwhelmed by the tide and complaining that the rest of the world is leaving it to them, have been thrusting the Cambodians back.

So much sympthy has been expressed for the Cambodian people by Americans of all political persuasions over the years that you would think the United States would now be bursting to help the particular Combodians who, by approaching the Thai border, have come near range of American help. But legislation enacted in the heat of other moments crimps a decent American response now. The American government cannot deal directly with either Heng Samrin or Pol to reach the people in need. Food aid can be channeled to or across the Thai border through private or international organizations, but only if -- some difficult ifs -- the aid does not go through the Cambodian government, it meets the immediate requirements of needy people, and it does not confer any long-term economic benefit. Talk about threading a needle.

The needle should, of course, be threaded. Decency to a brutalized people requires no less. And the food-aid law should be changed to permit the flexiblity suitable to changed political circumstances. It cannot be countenanced that the Thais continue to throw helpless Cambodians back into the pit. An effective response on food may help convince the Thais that their pleas for sharing the burden have been heard.