THE STEPS he has decided to take in the wake of the Soviet invasion of Afghanistan, says President Carter, "will require some sacrifice on the part of all Americans." Exactly so. He has understood, as we trust an increasing number of Americans do, too, that nothing will bring its folly home to the Soviet Union that does not involve "some sacrifice" by Americans. His estimate is that Americans accept the gravity of the Soviet aggression -- for the threat it poses to a sensitive region and for its dramatization of Moscow's readiness to violate the international order -- and will do what is necessary. We think his speech Friday evening contributed significantly to mustering the support on which "sacrifice" must necessarily be based.

Of the announced economic sanctions, the chief one is to hold back sales of an additional 17 million tons of grain beyond the 8 million committed. This grain would have gone mainly to feed the animals that supply the improved diet the Kremlin has long promised its drably fed people. Withholding the grain will not inflict hunger, but it will carry a message to every Soviet family. The Iowa caucus aside, equity required Mr. Carter to ensure that the brunt of the burden would not be borne by American farmers alone. This he did by indicating ways -- chiefly through the federal budget -- in which all Americans will share the cost. Mr. Carter also reported his "confidence" that the other principal grain exporters, all of them our allies, would not take up the slack. This is basic to the success of the sanction. It means, too, a gratifying making of common cause by allies whose understanding of their own stake in the alliance has not always been fully evident.

Mr. Carter's warning that American participation in (and attendance at) the Olympics is now in doubt invoked another aspect of "sacrifice." Many of us would sooner pay our share of the grain decision than lose the chance of field and watch American athletes in Moscow. It is precisely because the disappointment to Americans would be so keen, however, that withdrawal would have so great an impact on the Soviets. They crave the legitimacy and prestige (and money) conferred by playing host. To grant those boons, just as they have assaulted the foundations of the international system, would be obscene.

The diplomatic initiatives announced by Mr. Carter have no similar personal content, but they are no less important from the viewpoint of their intended effect on the Kremlin. The president offered arms and other aid to Pakistan -- we hope he will do this in ways consistent with regional stability and nuclear non-proliferation. He said he is ready to offer similar help to "other nations in the region": if Iran releases the hostages, it becomes eligible for help that could be vital in staving off Soviet pressures. Further developments are expected from Defense Secretary Harold Brown's trip to Peking. SALT, meanwhile, is on hold.

To survey Soviet-American relations now, and to compare the picture with Mr. Carter's expectations of three years ago, is a depressing exercise. Yet the Kremlin has given Mr. Carter, and the American people, no reasonable alternative. Mr. Carter went at least halfway with Moscow; many Americans thought he went too far. He was prepared to pay a personal price in his political standing but, with the latest Soviet move, he could not allow the United States to pay a national price. He came to his current view of the Kremlin with evident pain and regret. In asking Americans to support steps that "match the gravity of the Soviet action," however, he has made the right choice.