SUMMITS USED to be regarded as potentially great and pivotal events, or at least as stages on which Soviet and American political leaders could walk tall. But the generally deflating experience of nearly 20 Soviet-American summits since World War II has schooled the public to trim these expectations. Chief executives are now asked not much more than to deal with the business at hand and to leave things no worse than they were before.

The Kennedy-Khrushchev summit in Vienna in 1961 did not even achieve that minimal objective. On the Soviet side it produced an apparent perception that the United States, or at least its young president, could be pushed around and, on the American side, a second perception that the Soviets had to be disabused of that first one. In all too real a sense, the two countries have not progressed beyond that first Vienna summit. Soviets still seem to believe, or so many Americans fear, that they can bring their growing power to bear to their own advantage. Americans still seem to doubt whether their own power is enough to sober the Kremlin. Over the Vienna summit that opens tomorrow hovers the ghost of one that took place in 1961.

Jimmy Carter, unfortunately, has aggravated the problem. The problem is one of credibility. Whether the Russians lack respect for him is arguable; perhaps they have their own debate. It is clear, however, that many Americans are uneasy at his going off to deal with the Russians. Sen. Henry Jackson's summit-eve warnings of "appeasement" merely underline the point. Mr. Carter has not built much confidence in either his personal bargaining abilities or his vision of how the United States should adjust to a world in which it is no longer undisputed No. 1 and the Soviet Union is coming on strong. Leonid Brezhnev is ailing, and the agenda seems to be short and set and so there may be little room for presidential free-lancing.Mr. Carter may find this personally frustrating, but it is not the worst thing that could happen.

One subject dominates this summit: SALT. Neither Mr. Carter nor Mr. Brezhnev can be sure of staying in power long enough to guides SALT III, but they share a surpassing political interest in consolidating SALT II. That means going beyond the signing of a treaty and agreeing on maintenance of a political context that will help SALT II be ratified. Unquestionably this reequires the Kremlin, whatever the contrary temptations, to stay on good behavior for the duration of the American ratification debate. It may require Mr. Cater to offer what assurances he can that the treaty he receives back from the Senate will be essentially the one he negotiated, not an amended version. Otherwise there will be a "Soviet ratification debate" whose outcome is likely to please only those Americans who think the United States is better off without any treaty acceptable to Moscow.

There is a debate in this country and around the world about Moscow's ultimate political and strategic intentions. There is also a debate about whether the United States can conduct a responsible long-haul policy whithout fits of withdrawal and starts of interventionism. Neither of these debates can be effectively resolved at Vienna, but Mr. Carter can make his own modest but useful contribution there by pursuing a steady course.