WASHINGTON — Compared to the polar bear, the American pika is downright tiny.

Weighing only 4 ounces to 6 ounces, this small, rabbitlike mammal with thick brown hair that lives on boulder-covered slopes near alpine meadows in Western mountain ranges could represent the latest effort to use the Endangered Species Act to combat global warming.

Environmentalists filed a lawsuit Tuesday in U.S. district court in Sacramento, Calif., to force the Bush administration to decide whether to list the pika for protection under the act. The lawsuit claims the animal is threatened by rising temperatures and says the U.S. Fish and Wildlife Service has dragged its feet for months on whether to list it.

In May, the polar bear was protected as a threatened species under the act. But Interior Secretary Dirk Kempthorne made clear at the time that the Endangered Species Act was not intended to regulate global climate change.

Kempthorne said it would be "inappropriate" to use the Endangered Species Act to control greenhouse gas emissions from automobiles, power plants and other sources. He said the polar bear listing would be accompanied by "administrative guidance" and an administrative rule to limit any unintended harm to the U.S. economy.

Environmentalists dispute the White House approach.

"We disagree with the administration that the Endangered Species Act isn't a perfectly appropriate act to address global warming," said Greg Loarie of Earthjustice, an environmental legal firm representing the Center for Biological Diversity in the lawsuit.

Loarie said the pika (PIE-kah), which is intolerant of high temperatures, is an appropriate animal to test their contention.

"The pika is very much the polar bear of the Lower 48," he said.

The Fish and Wildlife Service had no comment on the lawsuit.

In addition to the polar bear, Loarie said, a type of coral and the Antarctic penguin are the only other species linked to global warming and the Endangered Species Act.

The pika's range includes the western U.S. and Canada in the Rocky Mountains from New Mexico to British Columbia, the Great Basin and the Sierra Nevada in California through the Cascade Range in Oregon and Washington.

More than a third of the documented pika populations in Nevada and Oregon have disappeared, and elsewhere they are moving upslope to avoid rising temperatures, said Shaye Wolf, a biologist with the Center for Biological Diversity. They can die when exposed to temperatures of 80 degrees Fahrenheit or higher for a few hours, Wolf said.

"The pika is the American West's canary in the coal mine," Wolf said. "As temperatures rise, pika populations at lower elevations are being driven to extinction, pushing pikas further upslope until they have nowhere else to go."