Lester Brown looked out of the seventh-floor window of his downtown office to the street where the last of the leaves are gold and brown and to the roof across the way shining with the new solar energy apparatus, and asked me matter-of-factly, ''Did you know that at the present rate of soil erosion our civilization can't continue?'' I told him no, I didn't know that, but that I thought it was interesting. So he marked with red a passage in his new book, ''Building a Sustainable Society,'' just issued by Worldwatch Institute, a private foundation he heads. It said:
''A world that now has over four billion human inhabitants desperately needs a land ethic, a new reverence for land, and a better understanding of the need to use carefully a resource that is too often taken for granted. Civilization cannot survive a continuing erosion of the cropland base or the endless conversion of prime farmland to nonfarm uses.''
Lester Brown has been studying that for a long time now, even before the 10 years he put in at the Department of Agriculture, when he was in India in 1956 - an eager 22-year-old on a Farm Youth Exchange Program. Now he is president of his own foundation which pours out books and pamphlets and warns that the rate of ecological change is accelerating.
''For example,'' he says, ''if you had been a demographer in 1970 and told them that at the end of the decade the country would be getting more energy from firewood than from nuclear power what would they have said? They would have dismissed you at once.''
''But why would I say a silly thing like that?'' I protested.
''Why, it's true,'' he said. He was off red-penciling my book again. ''Here, '' he said, ''read this.'' I did (gagging over the ''gigawatts'').
''Taking into account developments (in nuclear power) in late 1980 and early 1981, year 2000 consumption may not exceed 115 giga-watts (a gigawatt equals 1, 000 megawatts; a megawatt equals 1,000 kilowatts; a kilowatt equals, oh, you know that) scarcely a tenth of that projected by the Atomic Energy Commission in 1972.
''Ironically, by 1980, firewood had eclipsed nuclear power in the US energy budget - and despite the $36 billion government subsidy given the latter.''
Lester Brown, normally a quiet, academic type, held me with the beady eye of a traffic officer daring you to jump a yellow light. This was important; this was vital; this was food or famine for millions. But I knew the scenario already , or at least I knew it intellectually. It is hard to accept it emotionally. (A few students reject the postulates.) North America certainly has become the world's breadbasket in just the last few years. We all know how things are changing: oil shortage, for example - gasoline that used to cost 25 cents a gallon is now $1.50, and double that abroad. And population is going up all the time with rich and poor nations meeting last week in Cancun, Mexico, to think about it. The Lester Brown book is about that sort of thing, set down in chilling detail.
Here is where the red pencil marked three strokes for emphasis:
''As recently as 1950, for example, North America and Latin America had roughly e-qual populations - 163 and 168 million respectively. But while North America's population growth has tapered off substantially since then, Latin America's has escalated.'' Yes, he says, population of some countries has jumped 3 percent a year; if North America's had zoomed like that we would have absorbed the exportable food surplus ourselves and left none for anyone else. Instead, over 100 countries now rely on North America for grain.''
It goes on and on like that for 433 pages - forests, soil, wind-energy, solar energy. Are we going to protect our natural resources? After a while there is an odd excitement: keep your eye on Small Planet Earth, a tremendous struggle is going on there! Let's take that topsoil alone for a minute: you see ''millions of Ethiopians struggling for survival; scratching the surface of eroded land and eroding it further, cutting down the trees for warmth and fuel and leaving the country de-nuded . . .Over one billion - one billion - tons of topsoil flow from Ethiopia's highlands each year.'' (That's a report from a US AID mission.)
But that's Ethiopia! So how about that lovely black earth in Iowa; good soil that you can put your hand into and let it run through your fingers? Why, say agricultural studies, it pays better for the moment to work the soil to the limit with overgrazing and overplowing and not invest money in erosion-control practices and terracing and grading and things like that. Mining the soil, Lester Brown calls it. Some can think ahead but the immediate profit is in big crops right away.
Lester Brown sends a shiver through you in his cool prose. So what happens next? It's a continued thriller. See the next chapter.