The Bush administration altered critical portions of a scientific analysis of the environmental impact of cattle grazing on public lands before announcing Thursday that it would relax regulations limiting grazing on those lands, according to scientists involved in the study.

A government biologist and a hydrologist, who both retired this year from the U.S. Bureau of Land Management, said their conclusions that the proposed rules might adversely affect water quality and wildlife, including endangered species, were excised and replaced with language justifying less stringent regulations, which are favored by cattle ranchers.

Grazing regulations, which affect 160 million acres of public land in the Western United States, set the conditions under which ranchers may use that land, and guide government managers in determining how many cattle may graze, where, and for how long without harming natural resources.

The original draft of the environmental analysis warned that the new rules would have a "significant adverse impact" on wildlife, but that phrase was removed. The BLM now concludes that the grazing regulations are "beneficial to animals."

Eliminated from the final draft was another conclusion that read: "The Proposed Action will have a slow, long-term adverse impact on wildlife and biological diversity in general."

Also removed was language saying how the rules changes could adversely affect endangered species.

"This is a whitewash, they took all of our science and reversed it 180 degrees," said Erick Campbell, a former BLM state biologist in Nevada and a 30-year BLM employee who retired this year. Campbell was the author of sections of the report pertaining to impacts on wildlife and threatened and endangered species. "They rewrote everything. It's a crime," he said in an interview this week.

Campbell and the other retired BLM scientist who criticized the rules were among more than a dozen BLM specialists who contributed to the Environmental Impact Statement. Others who worked on the original draft could not be reached or did not return calls seeking comment.

A BLM official acknowledged that changes were made in the analysis and said they were part of a standard editing and review process. Ranchers hailed the regulations as a signal of new openness from the administration.

"We're hopeful that some of the provisions will strengthen the public lands grazing industry, and give our members certainty in their business," said Jenni Beck of the National Cattlemen's Beef Association. "We are encouraged that this EIS demonstrates the benefits of grazing on public lands."

Livestock graze on public land in 11 Western states, including 8 million acres in California. The vast acreage is needed to support a comparatively small number of livestock because in the arid region topsoil is thin and grass is generally sparse.

Only 2 percent of the nation's beef is produced from cattle on public lands.

The new rules, published Friday by the BLM, a division of the Department of Interior, ensures ranchers expanded access to public land and requires federal land managers to conduct protracted studies before taking action to limit that access.

The rules reverse a long-standing agency policy that gave BLM experts the authority to quickly determine if livestock grazing is inflicting damage.

The regulations also eliminate the agency's obligation to seek public input on some grazing decisions. Public comment will be allowed but not required.

In recent years, concerns about the condition of much Western grazing land has been heightened by persistent drought which has denuded pastures in the most arid areas, causing BLM managers to close some pastures, and leading many ranchers to sell their herds.

The new rules mark a departure from grazing regulations adopted in 1995, under President Clinton and Interior Secretary Bruce Babbitt. Those regulations reflected the view of range scientists that a legacy of overgrazing in the West had degraded scarce water resources, damaged native plant communities and imperiled wildlife.

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Babbitt ordered the BLM to establish standards that spelled out when public lands are open for grazing, and for the first time requiring range specialists to assess each pasture to ensure it held enough vegetation to support both wildlife and livestock. It was the first time in more than 50 years that the federal government attempted sweeping reforms of how Western ranchers operated on public lands.

By 1994, studies from scientists at the Department of Interior and the Department of Agriculture persuaded government land managers that livestock grazing was the most pervasive threat to plant and animals in the arid West.

Some conservation groups seized on the studies to mount a campaign to eliminate public lands grazing altogether, prompting a backlash that accused environmentalists of engaging in "rural cleansing" that would drive families off the land, some of whom had been there since the 19th century.

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This week, environmentalists were sharply critical of the new rules.

"It's an explicit rollback," said Thomas Lustig, staff attorney for the National Wildlife Federation in Boulder, Colo. "What (Interior Secretary Gale Norton) did was take Babbitt's regs and found parts where they could put a hurdle in to undermine the reforms."

Officials with the BLM said the new rules represented a step forward in improving the agency's management of livestock grazing on federal land.

Bud Cribley, the agency's manager for rangeland resources, said the report was written by a number of specialists from different offices within the BLM. When it was finished, in November 2003, the agency believed it "needed a lot of work," Cribley said.

"We disagreed with the impact analysis that was originally put forward. There were definitely changes made in the area of impact analysis. We adjusted it.

"The draft that we published we felt adequately addressed the impacts. We felt the changes we did make were based on good science."

Most of the changes came in sections analyzing projected impact of the rules on fisheries, plant and animal health as well as water quality and quantity.

Former BLM hydrologist Bill Brookes, who assessed the regulations' impact on water resources, said in the original draft that the proposed rule change is "an abrogation of (BLM's) responsibility under the Clean Water Act."

"Everything I wrote was totally rewritten and watered down," Brookes said in an interview Thursday.

"Everything in the report that was purported to be negative was watered down. Instead of saying, in the long-term, this will create problems, it now says, in the long-term, grazing is the best thing since sliced bread."