Human depredation is destroying as many as 20,000 species of plants and animals a year, scientists estimate.

The problem is "second in importance only to the threat of thermonuclear devastation," writes Lloyd V. Knutson, an entomologist with the U.S. Department of Agriculture and an organizer of an international symposium here last spring on germ-plasm and biotic diversity.Germplasm refers to genes, the basic hereditary material of all living things. In combination, genes determine the millions of plant and animal species that make Earth such a diverse place.

While not all involved scientists share Knutson's apocalyptic view of dwindling biotic diversity, all agree that international action is required if long-term disaster is to be averted.

For plant germplasm, some organizational machinery is already in place, both internationally and nationally. The International Board for Plant Genetic Resources, for example, coordinates a worldwide network of centers for germplasm conservation.

Several nations have their own germplasm collections. The largest is the U.S. Agriculture Department's National Plant Germplasm System, whose scattered facilities hold some 365,000 plants or seeds representing about 8,000 plant species.

Plaintiffs from several nations have sued the Agriculture Department, charging present germplasm programs are "grossly inadequate" in the face of "a crisis of unparalleled magnitude and scope."

Henry L. Shands, coordinator of the germplasm system, acknowledges the $26 million-a-year program is "far from being adequate. Our budget is probably half of what it should be if we were doing an adequate job. We're doing a very minimal job at this point in time."

But the chief instigator of the suit, Jeremy Rifkin, president of the Washington-based Foundation on Economic Trends, is "out of tune with the realities of what is being done," Shands told National Geographic. "If he would join forces with us instead of filing lawsuits, and if he would go to the Congress and try to help us get money, we'd all come out ahead."

However inadequate the plant programs might be, they are far ahead of programs for animal-gene collecting. No international facilities have been established and none exists in the United States.

But a leading advocate of such a system, Keith E. Gregory, a research geneticist at the Agriculture Department's Meat Animal Center in Clay Center, Neb., says: "Factors to bring an organized effort into being might be as favorable now as they've been in my lifetime as far as development of a coherent animal genetic-resources program."

Complicating the issue of international coordination is the belief of some Third World countries that rich nations are using seed collections to exploit them.

Many species of plants and animals have come into the industrialized world from underdeveloped countries in the southern hemisphere. But tropical diversity is disappearing with clearing of land, overgrazing and cutting of rain forests.

"The way these modern technologies are being applied is resulting directly in the disappearance of a tremendous amount of biodiversity," says Rodrigo Gamez, a Costa Rican biologist who directs his country's program for conservation of diversity. "The lower the standard of living, the higher the diversity. The demands of developed countries set standards at the expense of the needs of the developing countries."

Declaring himself an optimist, Gamez sees political and economic solutions to Central American ecological problems, requiring support from industrial nations.

"There's no way we can solve the problems of preservation of bio-diversity if we don't have peace in the region," he says. "Even for us in Costa Rica, if we don't stop the current trends of development, there will be very little left for the next generation."

William B. Lacy, a University of Kentucky sociologist who is studying the ethics of biotic diversity, says the United States must take the lead and act immediately. Diversity, he says, is "part of our total assets. It's not only a means to an end, it's an end in itself. To erode that biotic diversity is to undercut our own essence, our own existence."

Shands looks beyond germplasm management to the ominous prospect of mass starvation as the world's human population gallops toward 8 billion by 2015.

"When we start looking at those big numbers, our genetic resources are not going to be able to do the job," he says. "It's going to take something much more drastic."