There is evidence, though it's by no means conclusive yet, that Americans' longstanding decline in confidence in their government is coming to an end. For the first time in nearly 20 years, more Americans express trust in the government than did two years before. That's a summary of findings of the University of Michigan's Institute of Social Research, which has been asking large numbers of Americans definitive questions on these subjects every two years since 1952. It is not clear that confidence in government will continue to increase as it did between the 1980 and 1982 elections. But the decline in confidence does appear, at least for now, to have been halted.

The America of the early 1960s was too credulous and too trusting of its government. But you don't have to endorse Jimmy Carter's malaise speech to agree that the corrosive cynicism typical of voters' opinions and politicians' rhetoric in the late 1970s has made government's tasks more difficult than they need to be. In the 1950s and early 1960s, confidence and trust in government tended to rise because of Americans' increasing education levels and affluence, or so political scientists believed. Yet beginning in 1964, confidence declined, although educational attainment and affluence continued to rise.

Now, between 1980 and 1982, the number expressing high levels of confidence rose from 23 percent to 35 percent and the number expressing low levels fell from 51 percent to 38 percent. This is not just an expression of approval of Ronald Reagan's programs: confidence rose among Democrats as well as Republicans, among those who favored increases in government services as well as those who favored reductions.

So the rise was not just a vote of approval but also a judgment of effectiveness. Mr. Reagan's administration has accomplished, if not exactly what he promised, at least what Republican administrations in the last 50 years have been expected to do: it cut inflation (or allowed the Federal Reserve to do so) at the cost of worsening recession. From the 1930s through 1964, the peak confidence year, Democratic administrations did a good job of stopping recession and the Republican administration did a good job of stopping inflation. Then they didn't. Is the rise in confidence the result of a return to predictability--a predictability lacking in the period beginning with the Kennedy assassination and continuing through Vietnam, Watergate, the two energy price shocks and the seemingly out-of- control inflation of the late 1970s?

Whatever the reasons for this rise in confidence, it is surely not self-sustaining. Nor, in truth, is it all that widespread yet. More Americans remained, in 1982 at least, on the negative end of the scale than the positive. By the standards of the early 1960s, the nation is still cynical about government's effectiveness and about the intentions of the people who run it. What is interesting is the evidence that even in what has become a negative climate of opinion, positive attitudes can grow. That wasn't always obvious.