ATLANTA — The woman who led the nation's public health agency in a post-Sept. 11 world of bioterrorist fears is out, her resignation announced in a Friday night e-mail to employees.

Dr. Julie Gerberding has resigned as director of the Atlanta-based U.S. Centers for Disease Control and Prevention, and will be replaced on an interim basis by a deputy as of Jan. 20, the day President-elect Barack Obama is inaugurated.

The e-mail obtained by The Associated Press that discloses the news was sent Friday night to employees of the U.S. Department of Health and Human Services, the umbrella agency over CDC.

Although an HHS housecleaning has been expected with the new administration, Gerberding's fate was somewhat unclear. The first woman to head the agency, Gerberding led the CDC through a post-Sept. 11 world of bioterrorist fears and was considered an effective communicator with legislators and the public.

In a November e-mail to staff, Gerberding said she expected she might be leaving her job after the Bush administration left office. But colleagues said she quietly had held out hope she would be allowed to stay on in the job.

Speculation that she might remain was fueled by Obama's selection of Tom Daschle to as HHS Secretary. Daschle, the former Senate Democratic leader, is from South Dakota _ like Gerberding. Last month, she issued a statement to the press praising Daschle and his "tradition of finding practical solutions to very tough problems."

But Friday's e-mail confirms she will indeed be leaving office, a CDC spokesman said.

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"As part of the transition process, the Administration requested resignation letters from a number of senior-level officials, including Dr. Julie Gerberding. This week, the Administration accepted Dr. Gerberding's resignation, effective January 20," CDC spokesman Glen Nowak said in a prepared statement.

Nowak said Gerberding was traveling in Africa on CDC business and unavailable for comment.

The CDC investigates disease outbreaks, researches the cause and prevalence of health problems, and promotes illness prevention efforts.

Gerberding is head of the CDC and its sister agency, the Agency for Toxic Substances and Disease Registry. The two have a budget of about $8.8 billion and more than 14,000 full-time, part-time and contract employees.

Gerberding receives a total compensation of $202,200.

The memo announcing Gerberding's resignation was signed by Rich McKeown, chief of staff for outgoing U.S. Health and Human Services Secretary Mike Leavitt. It said William Gimson, the CDC's chief operating officer, will step in as interim director as of the 20th.

Daschle has not announced a choice for a new CDC director.

Gerberding was named CDC Director in July 2002. She was a relative newcomer to the agency; she had only joined in 1998 to head the agency's patient safety initiative in the CDC's Division of Healthcare Quality Promotion.

She had become prominent in the fall of late 2001. In a post with the CDC's National Center for Infectious Diseases at the time, she emerged as a leading spokeswoman for the agency during the anthrax crisis in which letters containing a deadly, anthrax powder were sent to some politicians and journalists and perhaps others. Five people died in a wave of attacks that panicked a nation already shaken by the 9/11 airplane attacks.

The CDC Director at the time was Dr. Jeffrey Koplan, who had been appointed by President Bill Clinton. He had a prickly relationship with Bush administration officials. Koplan resigned in March 2002, saying it was time to move on.

Gerberding was selected by Tommy Thompson, the U.S. Secretary of Health and Human Services, who was impressed by her performance during the anthrax crisis. She entered office pledging to work closely with the Bush administration.

She was the agency's first female director, a status highlighted in several ways, including a profile in Vogue magazine that featured a full-page color photograph of her in a gray Chanel suit and white Marc Jacobs high-heeled shoes.

Gerberding was a highly visible spokeswoman for the government on public health matters, eclipsing officials like the Surgeon General and the director of the National Institutes of Health in visibility.

That was due in part to the scary, urgent nature of topics her agency dealt with, including SARS, food poisoning outbreaks and the threat of a deadly new type of pandemic flu.

But her tenure also proved controversial.

She instituted a large, morale-damaging re-organization of the agency that triggered an exodus of admired agency scientists.

The agency was criticized for being slow to respond to Hurricane Katrina and, later, to survivors' complaints about formaldehyde fumes in trailers that had been provided by the government.

And in 2007, she was criticized for going along with the White House's editing of her Senate testimony on the impact of climate change on health, which involved deletion of key portions citing diseases that could flourish in a warmer climate.