Barack Obama restored protections for endangered species today in a roll-back of one of the most contentious last-minute rule changes of the George Bush era.

"For more than three decades, the Endangered Species Act has successfully protected our nation's most threatened wildlife, and we should be looking for ways to improve it - not weaken it," Obama said today.

The rule change, which was made final in mid-December last year, left it up to government agencies to decide on their own whether new dams, logging or mining operations posed a threat to endangered species or their habitat.

The rule also said that a project's impact on climate change should no longer be a factor when taking into account its impact on wildlife.

The Bush-era changes amounted to rolling back the clock on 35 years of protocol.

Until the rule became final in December - about six weeks before Bush left the White House - it had been required to call on government biologists from the Fish and Wildlife Service or other agencies to deliver a threat assessment before giving the go-ahead to development.

Bush had argued such protections were a drag on the economy. In announcing his decision on Tuesday, Obama said he saw no conflict between development and protecting endangered species.

"Throughout our history, there's been a tension between those who've sought to conserve our natural resources for the benefit of future generations, and those who have sought to profit from these resources," he said. "This is a false choice. With smart, sustainable policies, we can grow our economy today and preserve the environment."

The directive issued today short-circuits the lengthy process ordinarily required for changing government regulations.

It was welcomed by environmentalists, and criticised by businesss groups who said the protections were an obstacle to road-building and other projects that could help get the economy moving again.

"The Bush rules would have allowed agencies with little or no wildlife expertise to make decisions that could mean life or death for animals like the polar bear," said Carl Pope, executive director of the Sierra Club, said in a statement. "Our wildlife are clearly in much better hands now. President Obama is bringing science back into decision-making."

Congressman Nick Rahall, who leads the House natural resources committee, also voiced support: "I wholeheartedly support the president's proposal to restore the protections for endangered species ... I think we know who would have been the winner in this fox-guarding-the-hen-house scenario advanced by the Bush administration, and it would not be the hens."

Some business groups said they were exploring the option of legal action against the Obama memo.

Obama has said repeatedly that he will let science drive his administration's policies on the environment.

The memo is the latest in a series of moves by the White House to undo Bush's legacy on the environment.

Obama has ordered the Environmental Protection Agency to review its refusal to allow California to regulate carbon dioxide emissions from cars.

The White House has also stopped a move that would have opened up land in natural parks - including Arches National Park in Utah - to oil and gas drilling.