Interior Secretary Dirk Kempthorne has declined an invitation to explain to a Senate committee why no decision has been made on additional protections for polar bears.The deadline for a decision on listing polar bears as a threatened species was January 9.

Conservation groups petitioned to list polar bears as threatened because their habitat, sea ice, is shrinking from global warming.

Democratic Senator Barbara Boxer of California, chairwoman of the Senate Committee on Environment and Public Works, on Thursday asked Kempthorne to appear at an April hearing.

In a letter Friday, an assistant secretary, Lyle Laverty, said Kempthorne may contact Boxer privately, but would not appear at a hearing until after the polar bear decision is made.

Boxer called that "wholly inadequate."