PROTECTING plants and animals from extinction would seem an idea all could embrace. Who would want to stand by while the grizzly bear or bald eagle became history? But the Endangered Species Act - a law the United States Supreme Court calls ''the most comprehensive legislation for the preservation of endangered species ever enacted by any nation'' - is under heavy political attack.
It hasn't worked, critics say, and it has become a bureaucratic nightmare and a threat to private property. The law's supporters respond that it has helped bring many species - including the bald eagle - back from the brink of destruction. And at a cost of less than a dollar a year per American to implement, they add, it's a bargain.
HISTORY: The ESA was signed into law by former Republican President Richard Nixon in 1973. It provides for the listing of ''endangered'' species (those ''in danger of extinction'') as well as ''threatened'' species likely to become endangered in the future.
Species are defined as subspecies like the northern spotted owl and specific populations (such as grizzlies, which are listed in the lower 48 states but not Alaska).
Under the law, no one may ''harass, harm, pursue, hunt, shoot, wound, kill, trap, capture or collect ...'' listed fish or wildlife.
US Fish and Wildlife Service regulations extend ''harm'' to include damage to a species' environment, where it significantly impairs behavioral patterns. The Supreme Court upheld this concept in June.
The law requires officials to designate ''critical habitat'' for species and also to design ''recovery plans.'' The recent reintroduction of wolves into Yellowstone National Park is an example of such a plan.
SPECIES DECLINE: Federal officials estimate more than 500 native species in the US have gone extinct over the past 200 years - half of those since 1980. The number of listed plants and animals has grown to more than 900 - with 4,000 ''candidate'' species waiting for consideration.
Only a few have been ''delisted,'' however. Critics say this is proof the ESA doesn't work; supporters respond that species recovery is a long process. Forty percent of listed species now are stable or improving.
There are many causes of species decline: overharvesting, toxic pollution, exotic species (like the zebra mussel) that crowd out natives. But the biggest problem may be habitat destruction. Since the 1700s, for example, the contiguous 48 states have lost more than half their wetlands to conversion and construction. Nearly half of all species listed under the ESA have wetland habitat.
But as often as not, endangered species habitat is found on private property. The government and private landowners have been able to work out cooperative arrangements. (An example is housing development in areas of southern California where a threatened bird called the gnatcatcher lives.)
Still, there are increasing conflicts over preserving endangered species versus protecting private-property rights. In some cases, the clash is sharpened by the general benefits a species can give: More than half of all prescription drugs in the US derive from wild species. And their habitats often help clean water supplies and provide oxygen.
Most people seem to see this, despite the current emphasis on budget-cutting and property rights. A Times Mirror poll found 75 percent of respondents agreeing that government protection for endangered species should remain the same or be increased.
POPULAR POLICY: There's also a sense that human-caused extinction is wrong. ''The Endangered Species Act protects us as a legislative Noah's ark,'' says Dave Willis, an environmental activist from southern Oregon. ''It's the closest secular equivalent we have to God's covenant with 'every living creature' at the end of the Noah story....''