Struggling with cancer, Mollie Beattie, the first woman to head the U.S. Fish and Wildlife Service, has resigned as director of the agency to focus on her recovery.

Interior Secretary Bruce Babbitt on Wednesday called Beattie "an inspiration and a bright light for all of us." But he said she had "concluded that, given her medical condition, she can no longer discharge the duties" at the agency.Interior officials said Beattie, 49, has been too ill to work during the past two weeks. She has battled brain cancer since last year, taking a medical leave to recover from surgery in December and returned to her job in April after a second operation.

"I have agreed with a heavy heart to honor her request to leave the department," said Babbitt in a message to Interior Department employees Wednesday.

A former natural resource and conservation official in Vermont, Beattie was named to head the U.S. Fish and Wildlife Service in 1993 at the beginning of the Clinton administration. Holder of a degree in forestry, she also has a degree in public administration from Harvard.

During her more than three years as director of the Fish and Wildlife Service, she worked hard to expand the federal refuge system at a time of unprecedented budget cuts. And she has been a strong defender of the Endangered Species Act.