Sen. Barbara Boxer (D-Calif.) said it was wrong that Kempthorne declined her invitation to appear before the committee.
The hearing went on without Kempthorne or any other administration official.
The deadline for a decision on whether to list Alaska's polar bears as threatened under the Endangered Species Act was Jan. 9.
Conservation groups petitioned to list polar bears as threatened more than three years ago because their habitat, sea ice, is shrinking because of global warming.
Boxer said Kempthorne and other administration officials were "ducking their responsibility to the American people" by delaying a decision on the bears and then failing to appear at a hearing to explain why.
Boxer said she was especially troubled because the administration did not hesitate to open a major bear habitat to oil leases.
The Interior Department opened a large area of the Chukchi Sea to oil and gas leases in early February, despite sharp criticism from environmentalists who note that one-fifth of the Arctic's polar bears depend on sea ice in their hunt for food.
A spokesman for Kempthorne declined immediate comment, but in a letter to Boxer, the Interior secretary said he respectfully declined her invitation to appear at the hearing because he was named as a defendant in a lawsuit filed by an environmental group over the polar bear.