The deadline was Wednesday, but the U.S. Fish and Wildlife Service said it now hopes to provide a recommendation to Interior Secretary Dirk Kempthorne in time for a decision by him within the next month.
The department has never declared a species threatened or endangered because of climate change, said Dale Hall, director of the Fish and Wildlife Service.
"That's why this one has been so taxing and challenging to us," he said.
Environmental groups that petitioned to protect polar bears, arguing that warming threatened their habitat, said they would go court to ensure a timely decision.
"We certainly hope that the polar bear will be listed within the next month," said Kassie Siegel, an attorney for the Center for Biological Diversity.
Listing polar bears as "threatened" with extinction could trigger limits on development, particularly oil and gas exploration and production, that could harm the animals. That listing is a step below "endangered," the most severe classification under the Endangered Species Act.
Kempthorne proposed the "threatened" listing for polar bears in January 2007, and under the Endangered Species Act that gave him a deadline of exactly one year for a final decision. Among other things, the yearlong period includes opportunity for the public to comment on the proposed listing.
The Biological Diversity Center, along with Greenpeace and the Natural Resources Defense Council, filed a petition more than two years ago claiming that global warming was eroding sea ice, the polar bear's primary habitat.
In September, the U.S. Geological Survey issued a report concluding that two-thirds of the world's polar bears, including the entire population in Alaska, will be killed off by 2050 because of thinning sea ice from global warming in the Arctic.