* Rice's appointment could mean more White House control
* Republicans have criticized Rice over Libya attack
* She is named to replace the departing Donilon
* Obama selects Power as U.N. ambassador nominee
President Barack Obama chose close confidante Susan Rice as his new national security adviser on Wednesday, increasing White House control over foreign policy and defying Republican critics of her handling of last year's deadly attack on a U.S. compound in Libya.
The hard-charging Rice, selected to replace low-key Tom Donilon in the post, is expected to play a high-profile role in defending Obama's foreign policy, particularly on the civil war in Syria. Obama has come under fire for his cautious approach in response to mounting evidence that President Bashar al-Assad used chemical weapons against rebels seeking to oust him.
Obama will nominate Samantha Power - a Pulitzer Prize-winning author, former White House aide and Harvard professor - to replace Rice as U.S. ambassador to the United Nations, White House officials said.
The selection of Rice will likely anger Republicans who have sharply criticized her role in the handling of last September's attack on a U.S. compound in the Libyan city of Benghazi that killed four Americans, including U.S. Ambassador Christopher Stevens.
Obama had been expected to pick Rice, 48, as national security adviser since she withdrew last December from consideration to replace Hillary Clinton as secretary of state amid the criticism by Republicans about Benghazi. She had been Obama's first choice to replace Clinton. The job instead went to John Kerry.
Obama will avoid a congressional fight, though, because the post does not require Senate confirmation. Rice will replace Donilon in July as the official who coordinates U.S. foreign policy from the White House.
Republicans accuse Rice of playing down the Benghazi incident for political purposes by initially describing it on Sunday TV news shows as the result of a spontaneous protest, rather than a terrorist attack.
White House spokesman Jay Carney defended Rice.
"Ambassador Rice went out to the Sunday shows and conveyed what was the intelligence community's best assessment of what had happened in Benghazi at the time," Carney told a briefing.
Under Rice, the conduct of foreign policy is likely to be centralized out of the White House, raising questions about how much leeway will be given to Kerry, said Aaron David Miller, a foreign policy scholar at the Woodrow Wilson Center.
"She's very direct, very outspoken, very tough but extremely skilled and confident, which makes her formidable," Miller said. "The fact that she's close to the president makes her extremely formidable."
The shakeup comes as Obama grapples with a welter of foreign policy challenges, from Syria to China's rise on the world stage, an issue that will be brought to the fore this week when Obama meets Chinese President Xi Jinping in California.
Power's selection for the U.N. post was a bit of a surprise. U.N. and U.S. diplomats had anticipated that Obama would choose Deputy Secretary of State Williams Burns.
This is a fresh chance for her after her discretion and diplomatic skills were called into question when she labeled then-Democratic presidential candidate Hillary Clinton - running against Obama at the time for the party's White House nomination - a "monster" in 2008. The remark prompted her resignation from Obama's campaign team.
Rice's critics were largely holding their fire. Republican Senator John McCain, a leading opponent of how Obama has handled the Benghazi controversy, tweeted that he disagreed with Rice's selection but that "I'll make every effort" to work with her.
Rice is one of the original members of the team that helped Obama win election in 2008, a victory in part won on his opposition to the Iraq war. She became the first black woman to serve as U.S. ambassador to the United Nations.
During her years at the United Nations, she acquired a reputation as a tough, often uncompromising diplomat who has no qualms about cursing behind closed doors.
One council diplomat told Reuters how he had seen an email message from Rice to another U.S. official about a proposed Security Council statement that simply said: "Let's kill this."
Some Security Council diplomats say that she has at times been overbearing, though they acknowledge that she has a good sense of humor and has been very effective in getting U.S. policies across at the United Nations in New York.
Obama has drawn scrutiny for taking a cautious approach to evidence that Syria used chemical weapons after declaring any such usage would cross a "red line." He has also been reluctant to take steps to arm the Syrian rebels or participate in a "no-fly" zone, to the frustration of the Syrian opposition.
Rice appears to be of like mind. U.N. diplomats familiar with her thinking say she has been extremely cautious when it comes to supporting Syria's insurgents with weapons and has backed Obama's reluctance to do so.
Rice's reputation took a hit over the Benghazi attack. She went on television days after the incident to say it appeared to be the result of a spontaneous demonstration by Muslims upset at an video that insulted the Prophet Mohammed.
It eventually became clear that Islamist extremists had launched the attack on the anniversary of the Sept. 11, 2001, attacks on the United States.
Republicans continue to pound the Obama administration for what many of them contend was a cover-up to protect Obama from political damage as he sought re-election last year. The White House denies any such effort. White House officials insist Rice's role in the Benghazi affair was small.
White House officials said there was nothing precipitous that prompted the shakeup now. Donilon had talked for some time about leaving the post and he was most recently in Beijing preparing the details of the Obama-Xi meetings later this week.
"Having overseen the transition to a new, second-term national security team and having made significant progress on the key issue the president asked him to take on, including China, it is a natural moment for Tom to depart," a White House official said.
Donilon's last tasks will be to help Obama through the Xi meetings as well as overseas journeys this month, to Northern Ireland for a Group of Eight summit, to Germany and then later, a visit to Senegal, South Africa and Tanzania, officials said.