The Bush administration has succeeded in reshaping the Endangered Species Act in ways that have sharply limited the impact of the 30-year-old law aimed at protecting the nation's most vulnerable plants and animals, according to environmentalists and some independent analysts.

The Bush initiatives, which have ranged from recalculating the economic costs of protecting critical habitats to limiting the number of species added to the protected list, reflect a policy shift that Interior Secretary Gale A. Norton calls the "New Environmentalism." Under this approach, federal officials have focused more on providing incentives to private landowners to protect the habitats of endangered species than on prohibiting human activity on those lands. While some environmentalists praise the incentive programs, they say these projects are not enough to protect animals and plants on the brink of extinction.

Federal officials have added an average of 9.5 species a year to the endangered list under President Bush, compared with 65 a year under President Bill Clinton and 59 a year under President George H.W. Bush. They have designated as "critical habitat" only half the acreage recommended by federal biologists. And they are transferring key decision-making powers from the U.S. Fish and Wildlife Service to other agencies with different priorities.

"Instead of taking the Endangered Species Act head on, the administration is working to destroy the effectiveness of it through executive rule changes," said Brian Nowicki, a conservation biologist at the Tucson-based Center for Biological Diversity, which promotes species conservation. "They can't just attack it outright, so they try to stop it out of the spotlight."

The law, long a lightning rod for political and legal challenges, has come under intense attack from landowners who say it deprives them of full use of their property, and the administration has strived to alter features that top officials describe as broken.

"It's a different way of looking how to administer the act," said Craig Manson, assistant secretary of the interior for fish and wildlife and parks. "We are putting our efforts on the up-front end of conservation, as opposed to the emergency listing end."

This shift comes at a time when congressional critics are reviving plans to seek changes in the act to make it harder to list endangered species and declare habitat off-limits. House Resources Committee Chairman Richard W. Pombo (R-Calif.) plans to bring two Endangered Species Act revision bills up for a vote by the month's end.

The act "has been a failure in terms of what its initial goals were, in terms of identifying and recovering species," Pombo said in an interview, adding the administration has applied some "common-sense" principles in recent years, but "they can only go so far and stay within the boundaries of the law."

Enacted under President Richard M. Nixon in 1973 with overwhelming support in Congress, the Endangered Species Act seeks to protect ecological diversity by preventing animals and plants from being driven to extinction by development pressures, hunting or trafficking, and it authorizes the government to set up conservation programs to restore species whose numbers have dwindled dangerously. The Fish and Wildlife Service Web site currently counts 1,074 animals and insects and 749 plants as endangered or threatened in either the United States or foreign countries.

Environmentalists have sued administrations -- including Clinton's -- for failing to move quickly enough to list imperiled plants and animals. Private property owners, by contrast, have complained that once a species or its habitat is listed, they lose the economic value of their land. While experts estimate the law has saved hundreds of species from going extinct, only 15 species have recovered to full health since its passage, according to the Fish and Wildlife Service.

The Interior Department's Manson, who has questioned in the past to what lengths the government should go in staving off the extinction of certain species, said the administration has committed $1.3 billion toward conservation. Last year, for example, the department awarded $82,500 to help five Long Island towns protect the threatened piping plover, a beach bird, through programs that will monitor nesting and protect the bird's eggs from predators.

"We view it as a major accomplishment and contribution to plover protection on Long Island," said Joseph Jannsen, coastal resources manager for the Nature Conservancy.

Although the conservation grants are popular across the political spectrum, other initiatives are more controversial. Academics and wildlife advocates, as well as some career federal officials, question recent proposals that would let the U.S. Forest Service decide whether fire prevention projects pose a threat to key species and allow the Environmental Protection Agency to make that call on pesticides. Such judgments have been the province of the Fish and Wildlife Service.

Jamie Rappaport Clark, who headed the Service between 1997 and 2001 and is now executive vice president of the environmental group Defenders of Wildlife, said having those agencies make such determinations was "like the fox watching the chicken house." Fish and Wildlife officials, she said, "have the continuity and knowledge about the species to make the decisions that are relevant to the Endangered Species Act."

John J. Fay, a biologist at the Fish and Wildlife Service's endangered species program, said the shift is "a little troublesome" given the two agencies' track records on endangered species, but added that it could work. "Will someone have to keep a close eye on it? Absolutely," Fay said.

Oliver Houck, who heads Tulane University's environmental law program, said Bush's appointees are "hostile to the Endangered Species Act" and prefer to rely on "PR and carrots" rather than enforce the law.

Interior officials have been aggressive in using economic analyses to question whether to designate critical habitat, saying the designations often do little to help species recovery. Under the law, the government is supposed to determine whether a particular habitat is essential to the survival of the species when it makes a listing decision. If officials see a need, they must designate the habitat as critical so future federal activities do not damage it.

Between 2001 and 2003 the government approved 41 million of the 83 million acres of critical habitat initially proposed by federal biologists, a recent National Wildlife Federation survey found. In habitat cases involving the Topeka shiner, an endangered minnow, and the threatened bull trout, the administration decided not to consider economic analyses that showed potential benefits to such designations. In at least one of those cases, Manson said, the analyses did not comply with federal guidelines.

In a case involving 15 vernal pool species in California last year, Manson and his deputy Julie MacDonald decided not to designate nearly 1 million acres that biologists had deemed to be critical habitat.

The National Wildlife Federation charged that the decision was based on an analysis that inflated the expense of the move by counting previously estimated costs stemming from the listing.

"This administration has set new records in terms of the perversion and distortion of science," said John Kostyack, the federation's senior counsel.

Manson responded that calculating economic costs was subjective, "a matter of policy judgment and how one sees it. . . . You get any two folks together and they will disagree on the values of benefits and costs."

Endangered species advocates have gone to court to press for more listings and critical habitat designations. Center for Biological Diversity conservation biologist Noah Greenwald has been seeking a listing for the Montana fluvial Arctic grayling, a member of the salmon family described in Lewis and Clark's journals in 1805 as "equally well flavored" as speckled trout.

In 1994, Fish and Wildlife Service officials determined that listing was warranted because the fish are a distinct population, but the agency lacked the money to proceed. The fish is now restricted to just 60 miles of river in Montana, where drought coupled with farming activity have drained the waterway to a trickle during summer months:Now there are barely enough fish to count, Greenwald said: "It's a grim situation."

But administration officials say they are also attuned to the pleas of farmers such as Joe Hopkins, a Georgia forester who could not legally harvest valuable heart pine timber on his land after a 2000 fire because it was home to the endangered red-cockaded woodpecker.

"I just had to watch it rot on the stump," Hopkins said. "I don't want to watch any species go extinct, but it's not fair to put it on a few private landowners to finance the Endangered Species Act."

Researcher Madonna Leibling contributed to this report.