Thomas Malthus would have loved it. Back in the late 18th Century, he predicted that world population would grow geometrically while food supply would increase only arithmetically. Mass poverty would result. In the same vein, the modern Malthusians see population rising unchecked and the earth's resources diminishing inexorably. Global scarcity impends, threatening economic, environmental or political calamity.

Only time will settle the issues raised by the modern Malthusians, but the suspicion here is that the truly scarce resource is not natural, but man-made: competent government.

Although some resources -- oil and food, most conspicuously -- are not as abundant as we would like, the prospects for increased production (food) or substitution (oil) are enormous. The real problem is that governments may not prove equal to the possibilities.

Even the United States followed -- and still follows, in the case of natural gas -- an absurd policy of wasting precious resources by maintaining artificially low prices. If the United States behaves so foolishly, what can be exptected of less experienced, less settled governments? f

The pressures for makeshift policies in many developing countries are awesome. During the next 20 years, the populations of many of these countries will nearly double. Failure to produce food or jobs risks upheaval just when governments need more stability.

A similar paradox applies to global politics. As economic and environmental problems spill across national borders, nations increasingly need to find common solutions. Yet troubled nations -- like troubled individuals -- become either introverted and suspicious or hostile and aggressive.

All this may explain today's fashionable pessimism. Within the past few months, we have had the following: a massive government study -- "The Global 2000 Report to the President" -- that foresees a "potential for global problems of alarming proportions" by the turn of the century; the World Bank's "World Development Report," which concludes that prospects for economic growth have deteriorated sharply; and a special issue of Scientific American on development that characterizes the past 20 years as "decades of disappointment."

You have to take some of this with a grain of salt. The gloom of the moment obscures considerable gains. By most measures, the material (if not the spiritual) lot of humankind has improved markedly in the past 30 years. Even in the lowest-income countries, life expectancy rose from 35 to nearly 50 years between 1950 and 1978, according to the World Bank. Per capita income in these same nations, though still appallingly low, increased from $164 to $245 over the three decades (measured in constant 1980 dollars).

It's also possible to be too pessimistic. The "Global 2000" report asserts, for example, that most potential farmland is already under cultivation. Writing in Scientific American, Nevin S. Scrimshaw and Lance Taylor, food specialists at the Massachusetts Institute of Technology, cite studies indicating the potential cropland may be 50 percent greater than today. They also echo what many farm specialists believe: Much production is now so inefficient that good management and technology can produce sizable gains.

If anything, the past decade has demonstrated that the world does adjust to a declining resource base when there are the right signals -- usually higher prices. Before 1973, the noncommunist world's oil consumption was rising by an average of 7 percent annually, which meant a doubling nearly every 10 years; between 1973 and 1977, that dropped to 0.6 percent, and it is probably lower now.

The industrialized world's demand for material goods also may be slowing, according to Ronald G. Ridker and William D. Watson Jr., two researchers for Resources for the Future Inc. here. They argue that at higher levels of prosperity, leisure becomes more important and saturation occurs in housing, autos and many consumer goods.

The counter pressure to this, of course, is economic growth in the developing countries. Here is one of the great contradictions. Prosperity seems to diminish population growth; better educated and more affluent families seem to want fewer children. But prosperity -- more than population -- creates demand for resources. The United States, with one-third of India's population, uses 21 times as much energy.

How all this works out is what the computer people play at. But the weakest reed in their projections is not the potential availability of resources but humankind's ability to develop the potential. The developing and developed worlds differ from each other not only in wealth but also in age. In developed countries, less than one-fourth of the population is under 15; in developing countries, the average is 40 percent.

As these children have children, most of the increase in the world's population in the next 20 years -- projected to rise from about 4.4 billion to 6 billion -- will occur in developing countries. Consider these World Bank estimates: India will grow from 672 million to 974 million, Indonesia from 142 million to 204 million, Brazil from 126 million to 201 million and Mexico from 70 million to 116 million.

When you look at these numbers, you realize that the problems confronting Western governments are trivial by comparison. Bringing new resources into production -- whether they be food or oil -- requires not only good policies and good luck but also a lot of time. But local population explosions don't allow much time. They increase urbanization and subvert old social structures. The danger of a chronic and reinforcing political instability is inherent.

Each nation has its own peculiar history, and many new countries are "nations" in name only. States with such short histories inspire ferocious competition for leadership. Today's economic and population pressures simply pile atop long-standing ethnic, regional, religious or tribal differences. Already, many developing countries are being whipsawed between regimes.

Westerners, particularly Americans, take stable, reasonably competent government for granted. In fact, it is a rare and precious asset that most of the world doesn't have.