UNLESS the international community can reverse the current trend in global biodiversity loss, the rate of extinction worldwide over the next few decades could rise to 1,000 times the normal background rate. The result could be the loss of up to half the species on Earth."The quote - which sounds like part of a fund-raising scare letter from an activist group - is from President Bush's 1991 report to Congress on environmental quality. It is a politically loaded statement - at the root of the growing debate about amending the Endangered Species Act of 1973. It is likely to be the key issue at the United Nations Conference on Environment and Development to be held in Rio de Janeiro next year, the first such meeting in 20 years. Before the meeting in Brazil or the legislative wrangle over the endangered species law, the United States Supreme Court will address the subject, and unfortunately the "environment president" seems to be on the wrong side. The issue is whether federal agencies involved in overseas development projects have to consider the impact on endangered species, as domestic agencies and private developers must do in the US. Two examples: The US Department of Agriculture is using pesticides in Guatemala harmful to an endangered bird (the golden-cheeked warbler) that migrates to and from Texas. The US Bureau of Reclamation is involved in China's Three Gorges Dam project, which will seriously impact the Yangtze River dolphin and possibl y affect panda habitat as well. The bureaucratic question is whether officials from such agencies should walk down the hall and talk to the US Fish and Wildlife Service before deciding to support such projects. Should the Voice of America take into account the endangered Eurasian peregrine falcon before it builds huge transmitting towers in Israel's Negev desert, in the middle of the second largest migrating bird flyway in the world? Should the US help fund forestry projects in Africa when they reduce the habitat of elephants whose num bers have been decimated by ivory poachers? Attorney John Fitzgerald of Defenders of Wildlife points out the irony of going ahead with such projects. "we're continuing the ravages of DDT in the Brazilian rain forest that's harmful to numerous resident wildlife up and down the food chain." And, he says, "it's bizarre to go through all kinds of contortions to halt the trade in African ivory and yet hit them at the other end by destroying their habitat." The Bush administration argues that forcing US development agencies to consult with the Interior Department on potential harm to endangered species amounts to interfering with another country's right to economic self-determination, and that seems to be the philosophical direction a growing number of countries are taking. Recently, a General Agreement on Tariffs and Trade (GATT) panel recommended that member nations agree not to enact controls on trade based on natural resource conservation outside their territorial jurisdiction. But that was not the intent of Congress when it passed the Endangered Species Act. The Eighth US Circuit Court of Appeals last summer declared that "viewed as a whole [the act] clearly demonstrates congressional commitment to worldwide conservation efforts." Any "radical shift" to exclude overseas projects (as the Reagan administration did and the Bush administration wants to continue) "runs contrary to that commitment," the court ruled. That is the ruling President Bush is appealing to the Supreme Court which the high court last spring agreed to hear. At last count, 11 states, a number of cities, and environmental groups from several other countries had sided with Defenders of Wildlife, Friends of Animals and Their Environment, and the Humane Society in fighting administration efforts to let US development agencies ignore the Endangered Species Act abroad. Among other things, they object to a policy that Mr. Fitzgerald calls "imperialism in the environmental sphere." In his report to Congress, Mr. Bush calls the United States "a world leader in meeting environmental challenges," and he says, "the conservation of biodiversity need be no different." The US, he goes on, "should be in the vanguard of nations facing this critical global challenge." Before continuing with a questionable policy regarding endangered species around the world, the president should reread those noble words.