Herman Kahn is happy again. Almost 15 years ago, the scholar-impresario of the Hudson Institute was publishing depressing books with titles like "On Thermonuclear War" and "Thinking the Unthinkable," trying to get people to look Doomsday in the face to see what color eyes it had.

Kahn's purpose, as he expressed it, was to avoid falling into the trap of thinking nuclear war couldn't possibly happen -- and thus to allow some naive policy miscalculation to precipitate it. There are still a lot of people who think that Kahn was altogether too fascinated by the subject. But so far Kahn's stare-downs with Doomsday haven't caused anybody to panic or pull the trigger -- and talking about nuclear war hasn't made it seem any less horrible.

So perhaps it is not surprising to find that Kahn is now eager to survey more pleasing vistas.

He sees, quite simply, a much pleasanter tomorrow. He thinks we are on the verge of a stable surge of world prosperity that will leave wealth and comfort much more widely distributed, that will ease humanity's burden and leave us living in a much gentler and amicable world.

Predictions are difficult, as physicist Neils Bohr once said, especially when they are made about the future. There doesn't seem to be much way of evaluating the worth of Kahn's prognostications, except to say that he seems to have marshaled some pretty good evidence on his side. One straw in the wind that might lend him some credence: When Kahn finished the book, the stock market was so depressed that he felt compelled to include a special introductory disclaimer saying he still had faith in his predictions. The week the book was published, the stock market had one of its biggest rallies in history. You have to compliment Kahn for at least sticking by his ideas.

Whatever problems we face, says Kahn, they are not beyond solution. Energy? We will probably "luck out," but still have to be careful to conserve and develop our resources. Environmental problems? Except for the long-range effects of weather modification and acid rain, none is really intractable. Technological side-effects? ". . . once the externalities are satisfactorily understood they will presumably be properly controlled, turning a problem-prone super-industrial economy into a largely problem-controlled one."

In any case, says Kahn--and this is the key insight of the book -- most of these dilemmas depend far more on the way we perceive them than on exactly what is being perceived. The main shift, he argues, is going to be in the social attitudes of Americans toward further progress. Toward the end of any long expansionary period, such as in the 1950s and '60s, "various self-styled idealistic groups drawn from the more affluent classes mobilize in protest against materialism . . . and various real and imagined defects of the society." These attitudes become an increasing drag on further progress.

But Kahn feels -- and it is hard to disagree with him -- that we are now bottoming out of these "no-growth" attitudes. Problems like energy and environmental damage that seemed insurmountable only a few years ago are now being regarded more as only the normal trials any society must undergo. "The fact that the country as a whole is learning to deal with many current problems is . . . one of the primary reasons we believe that many corrections--leading to a boom -- are on the way."

What Kahn sees is not so much a "reindustrialization" as a "re-Americanization of America." He is wary about suggestions for remodeling American society on the model of Japan. (And Kahn, who has traveled and written widely about Japan, is in a good position to say.) In particular, he is skeptical of efforts to combine business, unions and government into a kind of "America, Inc.," a vision "based pretty much on a misunderstanding of how the United States works -- and, to some degree, of how Japan works." Instead, he thinks the entrepreneurial, innovative and individualistic traditions in the American character can serve us as well in the future as they have in the past.

"The American system . . . has worked superbly," Kahn writes. "It has encouraged and supported an extraordinarily high level of personal freedom, spontaneity, and initiative, as well as created and maintained a high general level of affluence . . . Even if it has not worked so well in recent years, it has been a city on a hill and the last great hope of humanity, and can be again."

It has traditionally been the role of the prophet in a society to warn people of dangers during the good times, and to lift their spirits during the bad. If Kahn does not prove to be completely accurate in his predictions, he is at least playing the role of the prophet the way it should be played.