WASHINGTON (AP) — The White House on Tuesday shook-up its communications team, with Anita Dunn stepping down and an aide taking over President Barack Obama's vaunted messaging machine.

Dan Pfeiffer will become White House communications director and Dunn will became an outside adviser to Obama's White House, officials said. They expect the full transition to take place before the end of the year.

The officials spoke on the condition of anonymity to discuss personnel decisions that had not yet been announced.

Dunn, a seasoned political operative, advised Obama's presidential bid and helped shape its outreach efforts to female voters. She initially refused to move to the White House, saying she wanted to spend time with her family. But when the White House's first communications director, Ellen Moran, stepped down to take a job at the Commerce Department, Dunn came aboard on an interim basis.

Since moving to the West Wing, she has been a fierce defender for the administration, a top target of conservative commentators and led a fight with Fox News.

"The reality of it is that Fox News often operates almost as either the research arm or the communications arm of the Republican Party," Dunn said last month. "And it is not ideological... what I think is fair to say about Fox, and the way we view it, is that it is more of a wing of the Republican Party."

Pfeiffer is similarly aggressive in his defense of Obama, a position he occupied during the campaign. He rose from traveling press secretary to the communications director for the campaign and later transition. A loyal Democratic communications operative, Pfeiffer previously worked for Vice President Al Gore, former Sen. Tom Daschle of South Dakota and Sen. Evan Bayh of Indiana.

Obama and other administration officials initially considered Pfeiffer for the top communications job but instead brought in Moran and Dunn — both women — a communications and press operation that is otherwise heavy on males.

The personnel changes were first reported on The Washington Post's Web site.