WASHINGTON » Shaking up his national security team, President Barack Obama tapped diplomat Susan Rice as his national security adviser, defying Republicans who have vigorously criticized her faulty explanation about the attack on Americans in Benghazi, Libya.

"Susan is the consummate public servant — a patriot who puts her country first," Obama said while announcing Rice’s appointment today during a Rose Garden ceremony.

Rice will take over the top national security post from Tom Donilon, who is resigning after four years in the White House. Obama lauded the 58-year-old Donilon for having "shaped every single national security policy of my presidency," including the renewed U.S. focus on ties with Asia.

The president also announced the nomination of former White House aide Samantha Power to replace Rice as U.S. ambassador to the United Nations. Power is a human rights advocate and expert on genocide.

It’s unclear whether the changes signal a significant shift in Obama’s foreign policy, particularly in Syria, where the U.S. is being pressured to act against President Bashar Assad.

Power is seen as a proponent of American intervention on humanitarian grounds and Rice backed greater U.S. involvement in Libya, though administration officials have made clear they don’t draw direct comparisons between the current situation in Syria and the 2011 push to oust Libyan leader Moammar Gadhafi. In that situation, the U.S. Britain and France maintained a no-fly zone to allow rebels to fight back against Gadhafi.

For Rice — a longtime Obama ally and close confidante of the president — the appointment is a bit of redemption after she was forced to withdraw from consideration as Obama’s second-term secretary of State amid criticism of her handling of the Benghazi attacks. Rice said at the time that she did not want her confirmation hearing to become a distraction for the White House. The national security post does not require Senate confirmation.

Neither Obama nor Rice mentioned the Benghazi controversy during today’s ceremony. Rice said she looked forward to working with lawmakers from both parties "to protect the United States, advance our global leadership and promote the values Americans hold dear."

Rice’s selection was greeted by a muted response from some Republicans who had earlier accused her of being part of an administration cover-up in the Benghazi attacks.

Arizona Sen. John McCain, one of Rice’s harshest critics, wrote on Twitter today that he disagreed with her appointment but would "make every effort" to work with her on important matters. And Tennessee Sen. Bob Corker, the top Republican on the foreign relations committee, said he had spoken with Rice and looked forward "to working with her on shaping important foreign policy and national security issues."

Rice, who first started working for Obama during his 2008 presidential campaign, has a close relationship with the president and many of his advisers. Her long-standing ties to Obama are expected to afford her significant influence within the White House.

The 48-year-old also served in various national security positions during the Clinton administration, including in key roles on peacekeeping and African affairs. Her world view is said to have been shaped by Clinton’s decision to not intervene in the Rwandan genocide, a move Rice said later deeply affected her.

Power won the 2003 Pulitzer Prize in general nonfiction for her book "A Problem From Hell: America and the Age of Genocide," which examined U.S. foreign policy toward genocide in the 20th century. She is a graduate of Yale University and Harvard Law School.

According to a biography on the White House website, Power also served as a professor at Harvard’s John F. Kennedy School of Government, where she taught courses on U.S. foreign policy, human rights, and extremism.

The White House official said Donilon is expected to stay on the job until early July, after Obama wraps up overseas trips to Europe and Africa, as well as an unusual summit in California later this week with Chinese President Xi Jinping.

Donilon has overseen a foreign policy agenda at the White House that put increased emphasis on the U.S. relationship with Asia. He’s also played a key role in the administration’s counterterrorism strategy, including the raid that led to the death of Osama bin Laden, and in managing the complex U.S. ties with Russia.