Critics say Bush is rushing through unpopular last-minute reforms
The Bush administration has made it easier for drilling, mining and major construction projects to go ahead without a full scientific assessment.
Revised rules mean agencies will no longer have to consult scientists about whether projects, such as the building of dams or mines, would harm wildlife.
Environmentalists say the changes could take away protection for animals and plants facing possible extinction.
Democratic President-elect Barack Obama has vowed to reverse the new rules.
Modifications to the Endangered Species Act (ESA) are expected to come into effect in about 30 days.
Republican supporters of the changes, along with developers and some federal agencies, argue the current system of environmental reviews causes delays to projects, pushing up costs.
Critics of President George W Bush say his administration is trying to rush through unpopular reforms during his last days in office, and correspondents say environmental groups are likely to challenge the changes in the courts.
The changes proposed by the Bush administration would let federal agencies make decisions on planned projects without a full scientific assessment as to their likely impact on the environment.
Under current rules, the impact of such projects must be assessed by experts.
The US interior department said the "common sense modifications" were a "narrow update of existing regulations" prompted by concerns the ESA would become a "backdoor for setting climate change policy".
"The rule strengthens the regulations so the government can focus on protecting endangered species as it strives to rebuild the American economy," said Secretary of the Interior Dirk Kempthorne.
"The Endangered Species Act is not the right tool to set climate change policy."
The White House has previously denied the late spate of rule changes is politically motivated.
Mike Daulton, a director of the National Audubon Society, an environmental group, urged Mr Obama and Congress to reverse the "destructive changes".
"The swan song of this administration is par for the course - special treatment for special interests at the expense of sound science and conservation."
Senior Democrats have questioned the "one-minute-to-midnight" rules which, if in place before Mr Bush leaves the White House, would be harder for Mr Obama to repeal when he takes office on 20 January 2009.
Mr Obama's chief of transition, John Podesta, has said the incoming president would review the last-minute actions, and seek to repeal those that are "not in the interests of the country".
Mr Bush has already been criticised by environmentalists for adding fewer than 10 species of plant and animals a year to the endangered list.
That contrasts with former President Bill Clinton, who added an average of 65 species a year.