LOS ANGELES — WHILE the world's eyes focus on the search for life forms billions of miles into space, environmentalists on Earth are increasingly questioning the ability of humans to sustain those they already know. In the 15 years since Congress passed the 1973 Endangered Species Act, one of the world's toughest wildlife preservation laws, 300 kinds of plants and animals have vanished from the United States while waiting for protection under federal programs. Nearly 1,000 became listed as endangered or threatened.
``The (Endangered Species) act has brought widespread attention to the issue, and a powerful law to address activities that adversely impact endangered species,'' says Steve McCormick, director of field operations for the California Nature Conservancy. ``Unfortunately, there are so many species to be listed, the law can't keep up.''
One major problem is the amount of money and time needed to review each case. Current funding can respond to only about 50 listings per year, not even denting the approximately 4,000 species on a so-called ``candidate'' list.
Extinction is Earth environment's ``norm'' according to some. ``Ninety-nine percent of the creatures ever to have come into existence have vanished,'' says a recent Newsweek cover story. ``To Mother Nature our contemporary infatuation with endangered species must seem callow sentimentality.''
NOT so, says the California Nature Conservancy, an environmental organization deftly and energetically trumpeting the evidence that mankind is at the opening stages of no less than an extinction spasm, having accelerated in 100 years to an extinction rate nearly 400 times ``normal.''
In the words of Oxford University's Norman Myers, this constitutes ``a mass extinction episode, in the sense of a sudden and pronounced decline worldwide in the abundance and diversity of ecologically disparate groups of organisms.''
One example is California, which is known in environmental circles as the epicenter of extinction in the continental US. The state has long been known as one of the most biologically diverse regions in the temperate world, with deserts lying in the long shadows of snowcapped mountains and northern old-growth forests that receive 100 inches of rain a year stretching to scorched valleys receiving less than 10.
Taking the nation's environmental pulse here requires some number crunching. The good news: California is home to 748 different kinds of fish, mammals, birds, reptiles, and amphibians, and 5,143 plants. Sixty-four of those animals and plants exist nowhere else on earth. According to a 1987 study by the Nature Conservancy, ``Sliding Toward Extinction,'' that number is more than in the entire central and northeastern US and Canada put together, a region 10 times as large.
But now the bad news: Almost 900 of those 5,891 plant and animal species are listed as endangered, threatened or rare, or in danger of becoming so.
``If we are really going to maintain our biological diversity, things need to be done very quickly,'' says Mr. McCormick.
The 1848 gold rush started the problem - the influx of great numbers of people. With new residents now crowding into California at the rate of 600,000 per year, the state's population is expected to reach 40 million by 2015, - impacting ranges, burrows, nests, dens, predation balances, air quality, vegetation, and all the rest.
``The study showed that what is happening in California really is of epidemic proportions,'' says the Conservancy's Kelly Cash. ``And given the increase in development and population as one of the fastest growing states, the trend is going to get worse. It paints a grim picture.''
The result has already been staggering. Since 1848, the state has lost 89 percent of its riparian woodlands, 80 percent of coastal wetlands, 94 percent of interior woodlands, and 99 percent of valley grasslands.
IN its report, the Nature Conservancy identified more than 200 species of animals and 600 plants facing the threat of extinction, only a third eligible for protection under the federal endangered species program.
Part of the problem with environmental number crunching is that people can't see or feel statistics. As part of its ongoing campaign to rouse the public from complacency, the Conservancy has decided to add faces to the numbers - 25 to be exact.
In a major photography exhibition that will tour the state for the next two years, 25 4-by-4-foot portraits will loom larger than life with ``don't-tread-on-me'' eyes, feet, tails, and scales. Objective: To remind viewers of the ephemeral character of our natural surroundings.
``This issue is simply not as apparent as drugs and crime to most people,'' says McCormick. ``We wanted to find a way for people who can't or don't get out there and see what's happening to be stimulated as to the problem.''
The yellow-billed cuckoo, giant kangaroo rat, magic gecko, brown pelican, and golden trout are five such creatures. The objective is to take museum-goers from the saltbrush scrub to the grassland plains to the freshwater marshes, to show how no corner of the ecosystem has escaped decimation.
Entitled ``The Vanishing Wildlife of California,'' the exhibit was codeveloped by the Nature Conservancy and the California Academy of Sciences and is the result of a two-year collaboration with well-known nature photographer Susan Middleton and an assistant, David Litschwager.
``The survival of any species is linked to successful stewardship of the habitats in which they occur,'' says Mary Ann Dunn of the Natural History Museum here, where the show's inaugural viewing runs through Sept. 17.
``This may be the last opportunity to preserve adequate habitats for perpetuation of California's endangered species,'' she says.