Safeguarding the world's treasure: its natural resources. The third world's push for economic development often undermines the local ecology. One country's ignorance or failure to prevent deterioration can lead to damage that knows no borders. This, plus increased environmental activism abroad, has started to affect US foreign policy.

AFTER a long search, the ``eco-navy'' aboard the aging and rusted fishing trawler found their target. They had been looking for the ship Sierra, known by many as a pirate whaling vessel. After the captain gave the order, the trawler closed in on the Sierra and rammed her. The conservation community, although determined to stop the killing of whales, condemned the move as a flagrant act of violence. The Sierra was rammed off the coast of northern Portugal in 1979 by a two-year-old group called the Sea Shepherd Conservation Society. Clearly, this group was different. Greenpeace members had become famous for their high-seas adventures, though always in a nonviolent manner. The Sea Shepherds, although a minority, represent the growing ranks of activists in the international environmental movement.

The rapid decline of whale populations, the destruction of tropical rain forests, the spread of hazardous wastes around the globe, and a host of other issues have finally caught the attention of the world community.

In the United States, conservationists aren't just talking about protecting natural resources within their own borders.

``We will build a fool's paradise here in the US if we focus only on our problems...,'' says James Gustave Speth, president of the World Resources Institute. ``It would be a huge mistake to continually work to improve environmental quality in the United States ... and neglect environmental quality and the resource base outside of the US.''

Several factors have influenced a growing acceptance of global issues:

There is a growing consensus within the scientific community on the need to act quickly to halt global degradation.

Grass-roots activists, and to some extent the general public, are turning to global issues.

Environmental organizations have embraced global agendas and are seeking to support indigenous conservation groups around the world.

There is a realization that environmental deterioration in other countries can adversely affect US foreign-policy objectives.

The United Nations, regional groups, and US government agencies are reevaluating third-world development projects and their effects on natural resources. Scientific consensus growing

The growing body of scientific evidence has been the most persuasive factor in elevating global issues. At a recent National Academy of Sciences symposium, scientists from around the world warned of dire consequences if the current rate of species extinction (some estimates as high as 17,500 a year) was not slowed.

A few years ago, such warnings were dismissed as alarmist by mainstream scientists. This developing consensus within the scientific community is strengthening the hand of environmentalists trying to push policymakers into action.

The last few years have seen a significant change in US foreign policy on environmental issues.

``We have come to recognize,'' says Ambassador Richard E. Benedick, deputy assistant secretary for environment, health, and natural resources at the State Department, ``that US national interests in promoting human freedom and economic growth can be undermined by instability in other countries related to environmental degradation, population pressures, and resource scarcity.''

Lester Brown, president of the Worldwatch Institute, reinforces this perception. ``For many countries, the greatest threats to security arise from ecological deterioration.'' He points to falling water tables, soil erosion, deforestation, and disappearing grasslands as indications that a nation may be pursuing a dangerous course. ``Ecological deficits pose greater long-term threats than economic deficits, since they actually diminish the resource base on which the productivity of the economy depends,'' Mr. Brown says.

Congressional hearings over the last several years have focused on adverse effects from large foreign-aid projects. The result has been numerous directives from Congress to the State and Treasury Departments to improve evaluation of World Bank projects.

Bank loans for huge dams, livestock, and agricultural projects have often resulted in massive environmental degradation. Relying on economic formulas that minimize pollution costs, pesticide use, and other environmental factors, leads to poorly designed projects that often fail, according to critics.

Even the Sierra Club, better known for its stand on US wilderness issues, has taken a high-profile position on World Bank projects. ``We are concerned,'' says J.Michael McCloskey, the club's chairman, ``because [bank] policies are the driving wedge for what happens to the environment in much of the developing world.''

For its part, the State Department appears to agree with critics of the bank. Secretary of State George Shultz, in an October 1985 cable to all US embassies, asked ambassadors to use their influence with host countries to emphasize that economic development that does not take into consideration wise resource management ``will be more costly and less productive in the long run....''

Last September, the State Department also urged ambassadors in Europe and Japan to push their host-country governments to support US efforts toward reforming world development projects.

International agreements dealing with environmental issues are also increasing. In addition to a recent meeting of world scientists in Geneva on protecting the earth's ozone layer, the State Department lists 50 ongoing multilateral agreements (17 more are in progress of negotiation), and more than 275 bilateral agreements (in over 70 countries) with at least some environmental component.

The agenda of international issues goes well beyond the World Bank.

Dr. Mostafa K. Tolba, executive director of the United Nations Environment Program, warns of ``a tremendous growth in urbanization which is completely uncontrolled, with no infrastructure and with the attendant environmental hazards and health problems.'' He considers these ``mega-towns'' one of the most critical problems facing the third world.

``The spread of the deserts, the destruction caused by polluted rain, the destruction of tropical forests, and the degradation of coastal ecosystems - home to 90 percent of all marine life - challenge the international community to find global solutions before it is too late,'' Dr. Tolba says.

The situation within developing countries is especially challenging. ``The poor are misusing the natural resources,'' he says, ``by plundering them to get food or at least a living, and the rich are overusing the natural resources, with the attendant waste and destruction of the resources.''

With no international authority to protect the global environment, activists have taken their stewardship role very seriously. Greenpeace is perhaps the most well known of these groups. Their intervention against whaling, seal kills, and nuclear testing has proved effective in raising public awareness.

In part because of Greenpeace efforts, the International Whaling Commission in 1985 issued a phase-out of all commercial whaling (Japan, Norway, the Soviet Union, Iceland, and South Korea continue, but each has committed itself to an eventual phase-out). A Canadian commission recently recommended a permanent halt to the commercial harp-seal kills, and protests over nuclear testing keep the issue before the public.

Paul Watson, a Canadian conservationist and founding member of Greenpeace, left the group a decade ago over disagreements on ``eco-violence.'' Not satisfied with passive interference, Mr. Watson prefers confrontation. He formed the Sea Shepherd Conservation Society in 1977, and is alleged to have been the captain in charge at the Sierra's sinking.

Watson's ship was then seized by Portuguese authorities, but before they could sell it, he secretly had it scuttled. When the Sierra was repaired, it was sent to the bottom with limpet mines. Before long, two other pirate whaling vessels met a similar fate at the hands of the Sea Shepherds.

More recently, Watson's group scuttled two Iceland whaling vessels, although they have since been refloated. It isn't uncommon for Watson's crews to be tear-gassed, beaten, and arrested; yet there is no shortage of volunteers. Rainforest Action Network

Randy Hayes is the director of the Rainforest Action Network, an organization he hopes will grow worldwide, ``far surpassing the whaling movement.'' The two-year-old Network, once headquartered in a San Francisco vegetarian restaurant, has already sponsored several national conferences on rain forest destruction and co-sponsored with Greenpeace a march on the World Bank in Washington, D.C., last September.

Environmentalists have focused on the tropical rain forests, since such forests harbor half of all animal and plant species in only 7 percent of the earth's land area. Every minute, another 100 acres is destroyed or seriously degraded.

One of the brighter developments reported by environmentalists working on international issues is the growing number of environmental organizations around the world. ``We are working with regional networks in Europe, Southeast Asia, Japan, Australia, and [smaller] ... groups in South America and the Amazon,'' says Mr. Hayes.

The creation of indigenous organizations will help overcome old arguments by some third-world governments and industrialists that environmental concern is a ``Western'' concept offered to restrain third-world modernization.

In addition, many environmental leaders now realize that every country must have its own conservation constituency.

World Wildlife Fund president William K. Reilly, in opening remarks at the fund's 25th anniversary meeting last September, explained that ``the citizens and institutions of countries ... hold the key to effective conservation of wildlife and wildlands within their borders. ... We now believe we can best foster conservation goals by supporting leadership programs in countries where our support will help the conservation movement become self-sustaining.''

Some environmentalists wonder whether the movement will be able to sustain citizen interest in global issues. Randy Hayes would like to see the rain forest issue grow like the antiwar movement of the late '60s.

Tolba asks, ``Why should the American citizen ... worry about something happening in a place called Zimbabwe or Nepal?'' Because everyone has a stake in the matter, he answers. ``We have to start worrying now about what the options are....''

Mr. Speth of the World Resources Institute agrees. ``We all have to find time to think about tomorrow, because we have more ability to affect tomorrow than we do today. ... Things can get a lot worse or they can get a lot better. And the choices have to be made today.''

Last in a three-part series. Previous articles ran Tuesday and Wednesday.