Crisis and conflict likely will shake the next two decades, according to two of America's generally most optimistic forecasters.

But after a rough ride through the end of the 20th Century, the U.S. and other industrialized countries should emerge, reordered and reinvigorated, into a new era of prosperity and pleasure.

In an ambitious article published today, Herman Kahn, director of the Hudson Institute think tank, and John Phelps, a colleague, warn of troubled times ahead for the world's advanced nations - a period of "malaise," they call it - marked by slower economic growth, potentially great violence and disorder, and vigorous controversy over societal goals.

The article, which appears in the June issue of The Futurist magazine, represents the first major statement on the world's loner-term economic prospects by Kahn, one of the country's best-known and controversial futurists. Crowded with graphs and tables that project events to the year 2200 and beyond, the article provides a sweeping look at what tomorrow's world economy may be like.

Its significance rests less in its detail than in its general view, and the authors say it was intended more to tease the imagination than to prove wholly right.

Basically, Kahn and Phelps see the world today as being in the midst of a "great transition" spanning 400 years and bridging the agricultural age to a post-industral one - an unstable period "that is neither fully healthy nor really sick."

"Two hundred years ago, almost everywhere human beings were comparatively few, poor and at the mercy of the forces of nature," Kahn and Phelps write."Two centuried hence, barring some combination of very bad luck and/or bad management, they should be numerous, rich and in control of the forces of nature."

For the moment, though, people and their governments - partcularly in the more developed nations - are likely to suffer complications and danger. The futurists predict that high inflation will persist, and the world economy system will remain very "vulnerable" to disruptions and slumps. Pointing also to the nuclear accident at Three Mile Island, they anticipate a prevailing "sense of technological crisis." They say social discontent also is likely to percolate in advanced nations.

"In the relatively affluent countries, both capitalist and socialist, we anticipate a sense of continuing uncertainty and malaise," Kahn and Phelps wrote.

The world still has several decades to go before its population and output growth rates reach their peaks, they assert. But the U.S. is said to have passed its zenith. Kahn and Phelps predict that output in the U.S. will grow at a much slower rate over the next two decades - 3 percent, slipping further to 2 percent in the 1990s, versus the average 5 percent of the postwar years.

In the meantime, the middle-income and poor nations are expected to set a more robust pace, enjoying growth rates of between 5 percent and 15 percent. Kahn and Phelps identify six "dynamic areas" of the world: Japan, the Asian rim countries (South Korea, Taiwan), part of Latin America (Brazil, Mexico, Venezula, perhaps other), eastern Europe, some emergent Mediterranean countries (Portugal, Spain, Yugoslavia) and most members of the Organization of Petroleum Exporting Countries.

They attribute the slowdown in the U.S., in part, to the rise of government and costs of regulation, and to the mounting intensity of international competition. They also blame new values and attitudes that have replaced former pro-growth ones.

In the U.S. today, there is "a disinclination to take risks and a loss of nerve, will and confidence," they assert, and further cite "excessive preoccupation" with a bevy of social concerns.

"Replacing the old 'square' values are new emphases on hedonism and self-fulfillment and new attitudes toward the family and society," say Kahn and Phelps. "There is a growing development of anti-technology, antigrowth attitudes; opinion polls show that about 70 percent of Americans admit to being influenced by 'small is better' and 'limits to growth' arguments."

The two futurists clearly have not been persauded by the new themes. Shedding their rather gloomy view of the short term, they don the optimism for which they are known and declare that technology will come to the rescue in the future as it has in the past.

They say current anxieties - sometimes bordering on panic - over problems that seem insurmountable today are unwarranted. They maintain that no major problem - whether energy, pollution, health or safety - will prove unmanageable.

"The potential for feasible technological fixes or solutions to important issues . . . is so often underestimated," they wrote, though admitting later to some degree of apprehension about the swift advance of technology. "Most of the new technologies are benign; unfortunately, some are rather threatening. 'Genetic engineering' in humans is one example of the latter."

They note that their long-range optimism "flies in the face of much currently fashionable conventional wisdom" - notably, the Club of Rome schoo, which argues that world population growth is generating pollution and depleting resources at a rate that threatens to strangle the globe.

Even during the next two bumpy decades, Kahn and Phelps foresee a continued rise in U.S. living standards. They predict an output per capita in this country of $14,000 by the year 2000, or about 45 percent greater than today.

They don't expect the gap between the rich and poor nations to narrow much over the next few decades. But they say that some time in the 21st century the world economy will stabilize at roughly 10 billion people and an output per capita of $20,000.

Kahn and Phelps see the world emerging eventually into a "post-industrial" era-a term coined by an earlier futurist. In that world, affluence will abound and only a relatively few people will have to work at the jobs necessary to keep the rest of the world fed and clothed. The others will be free to do whatever they wish.

To get from now to then, though, may be as much a matter of mind as anything else. "We need to develop various long-range images and scenarios to replace essentially negative and pessimistic views based on such dubious concepts as physical limits to growth, the widening income gap, the unmanageability of modern society, and the eroding quality of life," they wrote.