PHOENIX -- President-elect Barack Obama on Monday announced he has chosen Arizona Gov. Janet Napolitano to be secretary of the Department of Homeland Security. Napolitano's midterm departure will put Secretary of State Jan Brewer in the governor's office.

The turnover means the governor's office will change partisan hands -- Napolitano is a Democrat, Brewer is a Republican -- and comes as the state is grappling with a budget crisis that is expected to force significant cuts in spending.

"It is difficult to leave one job for another but one must go where one can best serve," Napolitano said during a news conference in Chicago with Obama and other newly announced members of his national security team.

The turnover of the Arizona governor's office to Brewer won't occur before early January at the earliest because Napolitano doesn't plan to step down as governor until the U.S. Senate confirms her appointment, Napolitano spokeswoman Jeanine L'Ecuyer said.

A Senate vote can't happen until Obama is inaugurated Jan. 20, though past presidential transitions have seen Senate committees hold pre-inauguration confirmation hearings.

In the meantime, the Legislature may have already held a special session on the budget this month and the Legislature will have started its 2009 regular session in mid-January. The launch of the regular session normally includes a State of the State address by the governor on the first day of the session and release of the governor's proposed budget within a week after that.

State Rep. John Kavanagh, R-Fountain Hills, said with a Republican governor, the GOP-controlled Legislature will have more cooperation in solving a projected billion-dollar deficit in the current fiscal year's budget.

"I think you'll see a Republican agenda of more fiscal responsibility" with Brewer as governor, Kavanagh said.

Napolitano, 51, would be departing after six years as Arizona governor and midway through her second four-year term. She previously served as Arizona attorney general and U.S. attorney for Arizona.

Brewer, 64, is a veteran public officeholder, with more than two decades as a legislator, a Maricopa County supervisor and secretary of state. Arizona does not have a lieutenant general.

Brewer had a reputation as a fiscal hard-liner and conservative on social issues while a legislator in the 1980s and 1990s, so her taking over the governorship would mean a new approach from Napolitano's direction.

As governor, Napolitano has pushed for more spending for education and social services. That drew support from advocates who welcome attention to areas they contended had been given short shrift in favor of tax cuts. However, Republican legislators charge that Napolitano rammed through spending that the state cannot afford.

Meanwhile, Napolitano was a liberal on some social issues, including abortion rights, and pushed for strong state action on environmental initiatives.

Citing the lack of any word from Napolitano, Brewer before Monday declined public comment on the prospect of becoming governor since it was reported in mid-November that Napolitano was Obama's primary choice for the homeland security post.

Napolitano's preprimary endorsement of Barack Obama in February was prized by his campaign as a nod from a female governor, and as a Democrat elected in a Republican-leaning state she was included in early speculation about possible running mates.

Also on Monday, Obama named former campaign rival Hillary Rodham Clinton as his secretary of state, and announced Robert Gates would remain as defense secretary, making President George W. Bush's Pentagon chief his own in the drive to wind down the U.S. role in Iraq.

Obama also introduced retired Marine Gen. James Jones as White House national security adviser and former Justice Department official Eric Holder as attorney general.