ANCHORAGE, Alaska — Alaska Gov. Sean Parnell says he has the best interest of polar bears at heart, but he doesn't intend to let the federal government's expanded protection for bears get in the way of the state's continued prosperity.

Like his predecessor, Sarah Palin, the governor is suing the federal government to overturn the listing of the iconic symbol of the Arctic as a threatened species, a move made last year that he believes could threaten Alaska's lifeblood: petroleum development.

"Currently some are attempting to improperly use the Endangered Species Act to shut down resource development," Parnell says. "I'm not going to let this happen on my watch."

SLIDESHOW: Flocke, the international polar bear celebrity

As Alaska North Slope wells dry up, the state is turning to potential offshore discoveries to refill the trans-Alaska pipeline and ensure the long-term prospects of a $26 billion proposed natural gas pipeline. Protections for polar bears under the Endangered Species Act could thwart that, Parnell says, adding that they are not needed.

"Alaskans have an excellent track record of both developing our natural resources and protecting our wildlife," says Parnell, who replaced Palin when she resigned in late July.

That's a position critics dispute after the 10.8-million-gallon (40.9-million-liter) Exxon Valdez oil spill in 1989, a 200,000-gallon (757,000-liter) North Slope pipeline spill in March 2006, and the state-funded killing of more than 1,000 wolves and hundreds of black bears since 2003 to increase moose and caribou populations.

Polar bears are regulated by the federal government like whales and seals. They spend most of their lives on frozen ocean water, where their main prey, ringed seals, give birth to pups in lairs. Warming of Arctic waters has significantly diminished the sea ice.

President George W. Bush's Interior Secretary, Dirk Kempthorne, listed polar bears as threatened in May 2008, eight months after summer sea ice levels melted to their lowest recorded level ever: 1.65 million square miles (4.27 million square kilometers), or nearly 40 percent below average since satellite monitoring began in 1979.

Most climate modelers predict a continued downward spiral, possibly with an Arctic Ocean that is ice free during summer months by 2030 or sooner.

The federal agency over two years however compiled an administrative record consisting of more than 175,000 pages including nine peer-reviewed scientific U.S. Geological Survey reports.

The most sobering conclusion: Projected changes in future sea ice will result in the loss of two-thirds of the world's current polar bear population by 2050, including all of America's. Researchers included the caveat that their assessment may have been conservative because Arctic sea ice decline likely was underestimated by the models used.

After the listing, Palin sued, saying the U.S. Fish and Wildlife Service's decision was not based on the best scientific and commercial data available as the law requires.

A month after he announced his full support for outer continental shelf petroleum development, Parnell said in October that the Endangered Species Act was being used as a "land use planning tool" instead of a species protection vehicle and the state filed new briefs in the polar bear lawsuit.

Alaska's lawyers will argue that the research was flawed, that federal officials looked too far into the future and that modeling is uncertain. Especially troublesome, Alaska Attorney General Dan Sullivan says, is that for the first time, the federal government listed a species with high population numbers — 20,000 to 25,000 worldwide, up from 8,000 to 10,000 in the 1960s.

"Never before has a species been listed when the population of that species is at its highest, most robust," Sullivan said. "It's at all-time historical highs."

The legal theory sets a dangerous precedent, he says, that could make Alaska the world's largest zoo with no additional benefit to wildlife.

"Any species that lives in an Arctic environment could be listed under the ESA without regard to the current health or size of the species population," he said.

Kassie Siegel, the attorney for the Center for Biological Diversity who wrote the original listing petition, expects the Alaska lawsuit to fail, saying state officials cherry-picked facts and ignored others.

Sport hunting in the 1950s and '60s dropped polar bear numbers to dangerously low levels and led to a 1973 international treaty that limited hunting, she said. Polar bears rebounded when hunting was controlled but have fallen again with sea ice decline, including animals in the two best studied subgroups, western Hudson Bay and Alaska's southern Beaufort Sea.

A 2006 USGS report estimated the Beaufort Sea polar bear population at 1,526, down from a previous estimate of 1,800 bears, a 15 percent decline. However, researchers said the study used different counting methods and the two estimates could not be statistically differentiated.

Siegel said an overall view of the research — declining cub survival, declining body size, diminishing sea ice — led to the listing decision, she said. Congress anticipated doubts but said decisions must be made on the best science, even if it's incomplete, she said.

"The agency can't just point to some remaining uncertainty and refuse to take action," she said. "We want the agency to proactively protect species under this law."

The stakes are high for Alaska. About 90 percent of Alaska's general fund revenue budget is fueled by the petroleum industry. The trans-Alaska pipeline is running at less than one-third capacity and only high oil prices and a new method of taxing oil production have kept Alaska from slashing government services or looking for other revenue sources, such as a state income tax.

In a decade or so, offshore gas production could be crucial for a new large-diameter pipeline, a project for which Parnell's revenue commissioner says there is no future alternative.

Questioned about the cost of fighting the federal government over the listing, Parnell says the cost of doing nothing was far greater.

"We're going to take every step we can to fight for Alaskan jobs and our economy," he says.