As a result, oil searches are too rushed and costly, industry officials say.

"The most troublesome challenge we see as an industry is the short operational window for North Slope exploration. It seems to get shorter every year," Jack Bergeron, Alaska manager for Total E&P USA, told the Anchorage Chamber of Commerce.

Environmentalists say the warming trend casts doubt on promises by the George W. Bush administration and other development boosters that oil drilling in northeast Alaska's Arctic National Wildlife Refuge would be limited to winter.

"When the going gets tough, the industry asks for exceptions," said Sara Callaghan Chapell, Alaska representative for the Sierra Club.

DRAMATIC EFFECTS

Alaska winters have warmed by at least 8 degrees Fahrenheit since the mid-1960s, according to University of Alaska Fairbanks scientists. In the Arctic, the effects are dramatic.

Bowhead whales and migratory seabirds show up sooner in springtime than they used to, say officials with the North Slope Borough, the local government for northernmost Alaska. Less sea ice hugs the shoreline, so storms bring bigger waves and more beach erosion. More permafrost thaws each summer.

"It's pretty noticeable to people who live up here," said Gordon Brower, a borough land-use specialist. "In some cases we've seen ice cellars cave in because it's just too warm."

Oil companies and government agencies are trying to adapt.

At industry's urging, and with funding mostly from the U.S. Department of Energy, the Department of Natural Resources has launched a study to rewrite the standard for tundra travel.

The state has long required six inches of snow on the ground and a foot of frost in the earth before heavy vehicles or equipment may be moved over the landscape.

That rule has been good enough to protect the fragile, slow-healing tundra, but may be too broad for modern conditions, said Harry Bader, study coordinator and northern regional land manager for the Department of Natural Resources.

"With global warming, we have actually lost half our winter work window," Bader said. "We need to be able to identify when the tundra is resistant to destruction more precisely."

TUNDRA PROTECTION

Researchers seek a more sophisticated way to calculate adequate tundra protection, considering a variety of factors like snow depth, snow-slab thickness, ground hardness, vegetation type and ambient air temperature, he said. A new model could be in place by late 2004, he said.

The study does not guarantee a longer season, he added. "We don't know what the results are going to be," he said.

Industry advocates say the state's current standard is too conservative. Regulators should be using flexible standards appropriate to varying local conditions, said Judy Brady, executive director of the Alaska Oil and Gas Association. "They're starting to find that one size doesn't fit all."

But environmentalists are concerned. "What we don't want to do is see the model pushed," said Arthur Hussey, executive director of Northern Alaska Environmental Center in Fairbanks.

Oil companies and the Energy Department are also investigating alternative technology, like insulation for ice pads, to stretch the drilling season.

One high-profile project is Anadarko's "Arctic Platform," a lightweight drilling unit on stilts 12 feet above the tundra.

"Arctic Platform could be the industry's next major step toward the day exploration and drilling would leave virtually no lasting trace on the surface," Michael Smith, assistant energy secretary, said earlier this year in a news release.