By Felicity Barringer

The polar bear, whose Arctic hunting grounds have been greatly reduced by a warming climate, will be placed under the protection of the Endangered Species Act, Interior Secretary Dirk Kempthorne announced Wednesday.

But the long-delayed decision to list the bear as a threatened species may prove less of an impediment to industries along the Alaskan coast than many environmentalists had hoped. While further protecting the polar bear from direct or immediate threats — like hunting — the Interior Department added stipulations, seldom invoked under the act, that will make it relatively easy for oil and gas exploration and development activities to proceed.

The decision builds on scientific evidence about the retreat of sea ice, which the bears use as a platform to hunt seals and as a pathway to the Arctic coasts where they den. But it does not directly link the threat to the bears to the build-up of greenhouse gases in the atmosphere.

Mr. Kempthorne said the Endangered Species Act was "never meant to regulate global climate change" and that it would be "inappropriate" to use the polar bear listing that way. He said he made the decision because "sea ice is vital to polar bears' survival," and scientific models show the rapid loss of ice will continue.

The secretary, who earlier in his political life was a strong opponent of the Endangered Species Act, added: "This has been a difficult decision. But in light of the scientific record, and the restraints of the inflexible law that guides me," he made " the only decision I can make."

Few natural resource decisions have been as closely watched or been the subject of such vehement disagreement within the Bush administration as this one, according to officials in the Interior Department and others familiar with the process. After the department missed a series of deadlines, a federal judge ruled two weeks ago that the decision had to be made by Thursday.

Barton H. Thompson Jr., a law professor and director of the Woods Institute of the Environment at Stanford University, said Wednesday that while the Interior Department gave itself "sufficient room" to list the polar bear, it did not provide "environmental organizations with a mechanism for trying to address climate change."

He said that lawsuits challenging the connection between a factory's greenhouse-gas emissions and the threat to individual polar bears might provide difficult to win.

"Interior has a reasonable case here that the connection is just too far removed," he said.

The provision of the act that the department is using to lighten the regulatory burden that the listing imposes on the oil and gas industry — known as a 4(d) rule — was designed to permit flexibility in the management of threatened species, as long as the chances of conservation of the species would be enhanced, or at least not diminished.

Kassie Siegel, a lawyer for the Center for Biological Diversity, one of three groups that originally sued to have the polar bear listed as threatened, said Wednesday that the decision was an acknowledgement of "global warming's urgency," but that it fell short of helping the polar bear.

"The administration acknowledges the bear is in need of intensive care," Ms. Siegel said. "The listing lets the bear into the hospital, but then the 4(d) rule says the bear's insurance doesn't cover the necessary treatments."

Last week, environmental groups said they were suspicious that the department would refuse to list the bear because of an agreement Mr. Kempthorne had announced with the environment minister of Canada. The agreement sets up an oversight body to monitor the status of various bear populations in the United States and Canada, and to "fill information gaps" and "establish baseline data" on the links between climate change and the health of bear populations.

Most of the 25,000 bears in the Arctic roam within Canada's territory; a scientific study issued by a Canadian group established to protect endangered wildlife said that 4 of 13 bear populations would most likely decline by more than 30 percent over the next three bear generations (or 36 years). One was the population off the Beaufort Sea, along the Alaskan coast. At least two others, the study said, were more threatened by hunting than by loss of sea ice.

M. Reed Hopper of the Pacific Legal Foundation, a property-rights group based in Sacramento, called the decision to list the polar bear "unprecedented" and said his group would sue the Interior Department over the decision.

He said the government had relied on "speculative computer modeling to justify" its decision, and that the listing would provide the polar bear little added protection.

"Never before has a thriving species been listed under the Environmental Species Act, nor should it be," he said.