SINCE THE PUBLICATION of Paul Ehrlich's The Population Bomb in 1968, Americans have generally become used to living in a "world of limited resources," in which the pressure of human numbers against the earth's "carrying capacity" was the planet's major social problem.

Certainly, there seemed to be occasional signs of hope. Pollution did seem to be abating in some instances. A country like India, once described by Ehrlich as a "basket case," suddenly turned into an exporter of food. Population growth rates have been dropping in Third World countries, so that it appears the nightmare of "wall-to-wall people" may be averted.

But none of these snippets of information has suggested anything more than a momentary stay against disaster. The intellectual framework for these problems --essentially a restatement of Thomas Malthus' original "dismal theorem" of population growth exceeding food resources--has remained unchallenged.

Julian Simon, an economist at the University of Illinois, squarely takes on this theorem in The Ultimate Resource.

Simon says that the framework popularized by the environmental movement is all wrong. We are not living in a world of limited resources. Paradoxical as it may seem, resources may be essentially infinite. The only limitation on them is the limit of our imagination in devising ways of using them.

Population growth, he says, is not a liability, but an asset. It is both an indication of growing prosperity, and a guarantee of future prosperity. The more people we have, the more human labor is available to tackle problems, and the more human minds there are to devise new ways of dealing with them. Our worry about population growth, he says, is a short-sighted view that sees new births only as dependent children. Once these new individuals grow up, they become contributing adults who help solve problems.

These are powerful ideas, if only because of their novelty in what has become the unquestioned frame of reference for our understanding of human life on the planet. Wherever portions of Simon's work have already appeared in print--in Science magazine in 1980, and in The Atlantic this summer--old environmentalists have come forth to denounce his perceptions.

They have good reason to be upset. The Ultimate Resource is the most powerful challenge to be mounted against the principles of popular environmentalism in the last 15 years.

On close inspection, none of Simon's theses turn out to be as fantastical as they may sound.

Take the matter of resources, for example. Our major error, he argues, is in thinking that we consume resources simply for the sake of using them up. In fact, we do it to provide ourselves with goods and services. True, we may eventually lay down so many telephone lines that copper wire starts to become exorbitantly expensive. But that only encourages us to switch to other resources. Now we are using glass fibers, whose principle element--silica--is the second most abundant resource on the planet. In addition, we launch communications satellites that, with a few square yards of aluminum, are able to handle phone calls that would have required thousands and thousands of miles of copper wire.

Individual resources may be finite, he argues, but our aptitude for using them is not. Human technology--our ability to make better and better use of what is available --is the real key. Our minds and imaginations are the "ultimate resource."

Simon demonstrates this through a simple but elegant mathematical analogy. When we think of "infinite" resources, he says, we tend to think of a line stretching over the horizon into infinity. Obviously, resources are not endlessly available in this way. But on any given line of finite length--one foot long, even--there are an infinite number of points. This is the way that resources are infinite. As we keep learning to slice the line thinner and thinner, there is no theoretical limit to how far we can go in using what we have.

Simon is not a lone, demented economist crying in the wilderness. Many other people have reached the same conclusions. In 1963, for example, Chandler Morse and Harold J. Barnett, two economists with Resources for the Future, published Scarcity and Growth, generally acknowledged as the definitive work in the field. After 10 years of study, during which they had looked for the opposite effects, Chandler and Morse wrote that they had finally come to the reluctant conclusion that resources are becoming less scarce all the time. This is because each generation, though using up a certain quantity of resources, leaves the next generation with an improved technology capable of tapping less-accessible resources. From all indications, they argued, this pattern --something we might call "human progress"--can go on forever.

Recalling Chandler and Morse's work, Simon points out that such optimistic appraisals--really quite common--are usually submerged by the doom-and-gloom pessimism of the neo-Malthusians. (Malthus himself, he notes, soon abandoned his own "dismal theorem," becoming very optimistic about humanity's abilities to solve its problems--something that is usually left out of the reprinted editions.) Books that express optimism about human progress, he says, tend to be checked out of the libraries about once a decade. Meanwhile, even the most scurrilous tract about the "population explosion" (such as one ex-military officer's evaluation of it as a "Communist plot") is worn out with use.

What Simon has attempted to synthesize are these many optimistic trains of thought in the existing literature.

The meat of his book is in the first half, where he presents his novel but thoroughly credible propositions that resources, pollution, and population growth are not overwhelmingly serious problems. The second half--an analysis of the anti-population-growth movement--is probably too long. Simon seems to be settling old scores. He was once an enthusiastic worker for Planned Parenthood, but quit when they adopted what he calls an "anti-natalist" stance.

Still, there is little in this book that can be ignored. What is most startling is its deep-rooted optimism about the human condition--a position that has not been seriously entertained in American thought for almost 20 years.

Whether its principles are widely accepted or not, The Ultimate Resource is a landmark book. It is going to have a significant influence on the intellectual currents of the 1980s.