As far as anyone knows, the Palos Verdes blue butterfly had only a few simple needs: a bit of meadowland to breed in and an ample supply of locoweed, the insect's staple food.

But by 1982, the butterfly was down to its last redoubt on the Palos Verdes peninsula just south of Los Angeles, where housing tracts and herbicides had wiped out much of its domain. When the city of Rancho Palos Verdes decided that year to turn the butterfly's seven-acre meadow into a baseball field, the butterfly quietly bowed out.

In the time it took a rototiller to churn up the new Fred Hesse Park diamond, the thumbnail-sized butterfly joined the passenger pigeon, the Carolina parakeet, the Penasco chipmunk and dozens of other North American creatures that will never be seen again. The latest to go was the dusky seaside sparrow, whose sole representative was an aging, half-blind male who died last June in Florida.

The sparrow and the butterfly are among the losers in what wildlife biologists and conservationists say is an increasingly desperate battle to save a nation's flora and fauna. Nearly 15 years after Congress enacted the Endangered Species Act, one of the world's toughest wildlife preservation laws, the failures are mounting faster than the successes.

In the last two decades, 300 kinds of plants and animals vanished from the United States while waiting in line for protection under federal programs. Nearly a thousand more are still waiting, their futures balanced precariously against budgetary constraints and a backlog of paper work.

The extinction rate in North America and other temperate zones pales in comparison to the massive losses occurring in tropical areas, where scientists estimate that 17,500 plants and animals are being wiped out annually.

But to conservationists and biologists, the steady erosion in the United States has become a national embarrassment and a nagging symbol of defeat.

"We can't even imagine saving the million-odd species that are likely to become extinct," said Peter Raven, director of the Missouri Botanical Garden in St. Louis and a leading authority on plant extinctions. "Eighty to 90 percent of those are in the subtropics, where extinction is proceeding rapidly. But we can make cuts at saving the 20,000 kinds of plants in the United States.

"The problem is that human responses only start when there are bodies in the street," he said.

In historical terms, there are more "bodies in the street" here than ever before. Despite some well-publicized successes, such as the resurgence of the American bald eagle and the modest comeback of the whooping crane, the continental United States has lost, by some estimates, more than 500 species and subspecies of native animals and plants in the 350 years since the pilgrims landed at Plymouth Rock.

For vertebrates, the rate of extinction is a hundred times higher than what scientists consider the "natural" rate, dwarfing the number of species lost during the Pleistocene ice ages several hundred thousand years ago. If plants and insects are included, the extinction rate soars, said Robert Chipley of the Nature Conservancy.

The reasons for the loss are varied, but they are almost always related to intrusions by man. Pesticides and pollution have taken a toll, as has overhunting for commercially valuable furs and feathers. But the prime problem remains loss of habitat as wild lands are converted to farms, tree plantations and housing developments.

The greatest losses have been in wetlands -- the rivers, lakes, swamps and coastal estuaries that are among the areas most densely packed with different species. When the nation was founded, it had 215 million acres of wetlands.

Now it has less than 99 million acres, an area about the size of California, and is losing that at the rate of 450,000 acres a year.

In the last decade, the United States has spent hundreds of millions of dollars in an effort to halt the loss of habitat and reverse declines in wild species; private organizations have spent millions more in educational campaigns.

Yet the California condor population is down to 27, only three of them females of breeding age. The black-footed ferret, given up for lost until a small colony was discovered in Wyoming several years ago, is back on the critical list after a devastating outbreak of disease.

California has lost the San Felipe leopard frog, Virginia its mountain mint. Henslow's sparrow no longer sings in Texas, and the phantom shiner has disappeared from Texas streams. Florida lost the pallid beach mouse; Hawaii lost more than a score of tropical plants found nowhere else in the world.

Even the grizzly bear, the enduring symbol of the American wilderness, is on the decline in Yellowstone National Park, where it has been protected for generations.

Conservationists blame the continued losses on what they consider a misguided policy of "biological brinksmanship." Unable or unwilling to take protective action on behalf of a species while it is still healthy enough to recover, they say, federal and state officials are waiting until the species is almost gone -- and then either give up or throw money at a lost cause.

"Too often we see delay when prompt action would make it possible, through a small investment and good management, to avoid these excessive costs," said John Fitzgerald of the Defenders of Wildlife.

In recent years, critics say, the main bottleneck has been the U.S. Fish and Wildlife Service, which is responsible for categorizing species as endangered or threatened, devising recovery plans for them and then carrying the plans out.

In 1981, with nearly 4,000 species waiting for review, the Reagan administration virtually obliterated the critical "listing" program.

Just four species made it on the list that year, largely because most candidates did not pass muster under a controversial cost-benefit analysis imposed by the new administration.

Since then, Congress has steadily pressed the service back into the listing and protection business. Last year, 45 species officially became eligible for protection, bringing the total to 455.

Interior Department officials acknowledge that the process is slow. "People say we study stuff to death, and maybe we do," said Frank Dunkle, director of the Fish and Wildlife Service. "But I don't think we have said, 'Hey, it'll cost too much money, so we can't do it.' "

Dunkle said each listing costs about $62,000, most of that for field studies and paper work. Current funding for the process is $3.2 million a year, or enough to list about 50 species annually.

At that rate, it will take the service 76 years to review the 3,800 species on its candidate list. More than 950 of those are in "category 1," meaning that there is already enough evidence to declare them threatened or endangered, but the paper work needed to provide protection has not been done.

"It comes back to money and people," Dunkle said. "If we had all the money in the world and there were no deficit, we could increase the percentage of listing. But I would think long and hard before I canceled law enforcement for listing."

Making the endangered list, however, is no guarantee of survival. The law forbids federal actions that may further endanger the species, such as dams and forestry projects, and can effectively block even private actions if they will result in the direct or indirect deaths of endangered creatures.

But the Department of the Interior has developed recovery plans for only about 55 percent of the species on the threatened or endangered list, and a still smaller percentage have plans actually being carried out.

The problem's ingredients include heated public opposition and cold, hard cash. The wildlife service triggered an outcry in Maine this year when it closed 1 1/2 miles of beach for the summer to protect two nesting pairs of endangered piping plovers. The beach was popular among nudists, who strongly protested.

At the other end of the scale, the cost of protecting the northern spotted owl -- a candidate for the endangered-species list -- may ultimately be $6 billion or more, according to estimates based on forestry industry statistics.

The owl makes its home in the Pacific Northwest's dwindling stretches of old-growth forest, where the trees have been untouched for at least 300 years, and experts say each pair requires from 2,000 to 5,000 acres to thrive. Given much less area, the birds may survive but do not reproduce.

The U.S. Forest Service has proposed saving enough old-growth forest to support about 550 breeding pairs, a fourth of the current population. The proposal has already been attacked by the timber industry because of the potential loss of billions of dollars worth of high-quality lumber. The idea is not much more popular among conservationists, who contend that the contemplated owl population is far too small to assure survival.

Interior Department officials and some outside scientists say the process is further complicated by political pressures, sometimes from elected officials trying to protect home-state projects.

Such was the case last year when Sen. Howell Heflin (D-Ala.) blocked reauthorization of the Endangered Species Act in response to the proposed listing of the Alabama flattened musk turtle. The turtle is dying out in the polluted waters of the Black Warrior River basin, and the state's coal industry feared it would be held responsible.

More often, Interior officials say, decisions about which species to protect -- and how -- are dictated by public pressure aimed at funneling money to a favored species.

Dunkle calls them the "warm and fuzzies" -- the furred or feathered animals that ride to the front of the list on a wave of Walt Disney sentiment and public television specials.

Efforts to save the California condor, for example, were running over $1 million a year, just for research, by the time the last of the majestic birds was trapped last year for a captive breeding program. The condor's last refuge, purchased after it became clear there would be no condors to use it for years, cost $6.7 million.

Conservationists defend the expenditures, partly on the grounds that efforts to save highly visible species help create a conservation ethic that will ultimately benefit lower-order animals and plants.

Some scientists tend to take a more hard-nosed view, suggesting that the big-ticket salvage operations are detracting from the broader goal of preserving biogenetic diversity: trees, in other words, that are obscuring the forest.

"It's not a matter of world survival whether the California condor lives," said botanist Raven. "Very possibly it will go extinct."

"Skip the moral and ethical reasons, and look strictly at the anthropomorphic reasons," said Stanford University professor Paul Ehrlich. "The reason we want these plants and animals is to exploit them, for food or for drugs. For that you need lots of population, lots of genetic diversity, lots of variability. You get down to a few in a zoo, then it's down to a question of esthetics.

"A lot of things waiting on the list are invertebrates and plants," he said. "Those are more important in terms of what mankind needs."

Consider, for example, the running buffalo clover (Trifolium stoloniferum). The clover was once abundant from Kansas to West Virginia, flourishing in the wake of bison herds that trampled its seed into the ground.

The six-inch plant lacks the majesty of a condor or the mystique of a Florida panther, but scientists believe it played an important role in creating the fertile land that became the nation's breadbasket.

Like all clovers and other legumes, the plant takes nitrogen from the air and stores it in root nodules in a form that other plants can use.

Scientists have been unable to coax greenhouse-grown specimens to form the enriching nodules, possibly because the soil bacteria that the running buffalo clover needed to thrive went the way of the bison. But its genes may one day be important in breeding new legumes, a class of plants that includes important food crops such as peas and beans as well as tropical trees that can fertilize the soil while providing food and fuel.

"There are 18,000 kinds of legumes in the world, maybe 1,000 in the United States," said Raven. "Next to the grass and the palm families, they are the most economically important plants in the world."

Important or not, the running buffalo clover is down to eight plants in the wild, muscled aside by other pasture plants and introduced species that have adapted better to the absence of the bison. It has not made the endangered list.