President-elect Barack Obama has decided to retain Robert Gates as defense secretary, signaling his desire to have operational continuity and stability in the Pentagon as the United States fights two wars in Iraq and Afghanistan.

The choice to keep Gates on board also fulfills Mr. Obama's campaign pledge to include a Republican in his cabinet. President George W. Bush nominated Gates, 65, to be Pentagon chief after Donald Rumsfeld resigned the post in November 2006.

At the press conference announcing the decision, Mr. Obama, as he did during his campaign, said he would give the military a new mission as soon as he takes office, which is "responsibly ending the war in Iraq through a successful transition to Iraqi control."

Gates said he was "mindful that we are engaged in two wars and face other serious challenges at home and around the world" and that he was "honored to serve President-elect Obama."

"I must do my duty as they do theirs," he said of the men and women in uniform in Iraq, Afghanistan and elsewhere. "How could I do otherwise?" Gates said.

In the lead up to Mr. Obama's announcement, some have said that the Pentagon, particularly in regards to the war in Iraq, needs new direction and leadership, and the decision to retain Gates belies Mr. Obama's campaign theme of change.

"I think it sends a bad message, because we do have capable individuals in the national security arena who can do that job. And the American people voted for change, and they voted for change across government," retired Gen. David McGinnis said on the NewsHour last week.

Others have argued that stability in the Pentagon's head office was necessary, even if policy decisions might change with the new administration.

"I think virtually everyone in Washington believes that Secretary Gates has done an excellent job as secretary of defense in a very difficult time period, and keeping him on is acknowledging that he's done well," Peter Feaver, who served on the National Security Council staff during the Bush administration, said on the NewsHour.

"[T]his is a very difficult time to be secretary of defense. There's a need for continuity. We're in the midst of two wars. And I think that appointing Gates or reappointing Gates sends a calming message," Feaver said.

Before becoming defense secretary, Gates was director of the CIA from 1991 to 1993. He was chosen for that position by President George H.W. Bush. Gates is the only career officer in the CIA's history to rise from entry-level employee to director.

"[T]his man has my full trust," the first President Bush said in his announcement. "He's honest. He's a man of total integrity."

Gates' confirmation hearings in 1991 were often contentious and lasted three weeks. He was forced to defend himself against two major charges: that he had lied to Congress in 1987 about his role in the Iran-Contra affair and that he politicized intelligence to suit the policy agenda of the Reagan administration.

Fifteen years later, Gates' confirmation as defense secretary went much smoother with just one day of questioning.

Gates joined the CIA in 1966, spending 27 years as an intelligence professional. During that time he spent nearly nine years at the National Security Council and the White House, serving four presidents.

A native of Kansas, Secretary Gates received a bachelor's degree from the College of William and Mary, a master's degree in history from Indiana University and a doctorate in Russian and Soviet history from Georgetown University.

In 1967, he was commissioned a second lieutenant in the U.S. Air Force and served for a year as an intelligence officer at Whiteman Air Force Base in Missouri.

-- Compiled by Tom LeGro for the Online NewsHour