FATHER HESBURGH, a three-star humanitarian and the president of Notre Dame, finds something unacceptable in the United States' selling the Soviet Union 25 millions tons of grain -- even as Moscow refuses to see that its client, Vietnam, delivers food to starving Cambodians. Father Hesburgh is right. He has identified a moral disharmony. How can the United States ship huge amounts of grain to the well-fed Russians, who buy it not to avert starvation but simply to improve the national diet, when the Russians assure the killing of hundreds of thousands of people in Cambodia?

At the United Nations, the Soviet ambassador, defensively refusing to join the nations pledging aid to Cambodia, notes that his country has provided 159,000 tons of food on its own -- to Vietnam's Cambodian puppets (and to Vietnamese soldiers in Cambodia). Compare those numbers: 160 times as much food is going from the United States to the Soviet Union as is going from the Soviet Union to Cambodia.

The minimal daily ration estimated to be necessary to avert widespread starvation in Cambodia is near 1,000 tons. That means that just from its American supplies, the Soviet Union could provide Cambodia's full emergency ration for a year and still have more than 24.5 millions tons left over. By dispatching to Cambodia only 1 to 2 percent of its American grain, that is, Moscow could rescue a threatened people.

It is tricky to use food for political ends. One wants to be reasonably humane and reasonably consistent. But some things can be said. It is a bad idea to starve a nation to extinction. It is a necessary idea to weigh continued food deliveries to a well-fed country like the Soviet Union whose government is helping starve another people to death.

Americans should not treat food as a conventional political counter. But Americans cannot treat food deliveries as morally neutral. Food means life. To sell it on a business-as-usual basis, to a country that is participating in a calculated food-denial policy of unprecedented cruelty is to condone death.