* Chooses tested veterans at critical juncture
* Biggest realignment of Obama war council to date
* President hopes to avoid internal divisions (Adds quotes and details)
By Matt Spetalnick
WASHINGTON, April 28 (Reuters) - President Barack Obama reshuffled his top national security aides on Thursday, altering the chemistry of a team that will help set strategy on the war in Afghanistan, turmoil in the Middle East and defense budget battles in Washington.
Picking tested veterans at a critical juncture of his presidency, Obama nominated CIA Director Leon Panetta to become U.S. defense secretary and named Army General David Petraeus, commander of the Afghan war effort, to head the spy agency.
The appointments mark the biggest realignment of Obama’s war council to date and could have broad implications for his administration’s plans to start withdrawing U.S. forces from Afghanistan in July and to seek deeper Pentagon spending cuts.
The shake-up also could give impetus to shaping the U.S. military role in the Libya conflict and to what has been dubbed the “Obama doctrine,” a still-evolving U.S. policy on how to respond to unrest sweeping the Arab world.
“Given the pivotal period that we’re entering, I felt that it was absolutely critical that we had this team in place so that we can stay focused on our missions, maintain our momentum and keep our nation secure,” Obama said at the White House with Panetta and Petraeus at his side.
Obama called for swift Senate confirmation of his nominees. Praise for the men from Democratic and Republican lawmakers alike suggested the process would go smoothly.
The changes were set in motion by the impending departure of Defense Secretary Robert Gates, a holdover from the Bush administration who had gained Obama’s trust.
The realignment raises questions about what kind of influence Secretary of State Hillary Clinton and Vice President Joe Biden, two of the administration’s most powerful foreign policy voices, will wield within the national security apparatus and how well the revamped team will work together.
Obama is taking a gamble that the personalities will mesh and he will avoid the bitter internal divisions that marked his lengthy deliberations on Afghanistan policy in late 2009.
With the U.S. public preoccupied with domestic concerns like high unemployment and rising gasoline prices, the last thing Obama needs as he seeks re-election in 2012 is another bout of bickering among his top aides over foreign policy.
In the 2009 Afghan policy debate, Clinton lined up with Gates against a group that included Biden and Panetta who were reported to have opposed Petraeus and his fellow commanders’ push for a troop-heavy strategy modeled on the one that helped turn the tide against insurgents in Iraq.
But Petraeus won Obama’s approval for increasing troop levels by 30,000 in exchange for assurances that a withdrawal could begin this summer to show Americans the makings of an exit strategy in the unpopular war.
Clinton, Obama’s former Democratic opponent who joined his cabinet in what was billed as a “team of rivals” approach, has had a close alliance with Gates.
One official noted that Clinton also has had deep ties to Panetta from his time as budget director and chief of staff for her husband, former President Bill Clinton, and this might boost her influence on national security matters. “She’s a tremendous fan, and they have worked closely together,” the official said.
Panetta, a longtime Democratic Party insider, is expected to oversee steady declines in Pentagon spending in order to divert weapons dollars to the Treasury Department to help reduce the U.S. deficit.
Petraeus is considered one of the top U.S. commanders, mixing political savvy with military know-how.
He was originally distrusted by the White House until he lowered his public profile, and his acceptance of the CIA post puts an end to Washington speculation that he be drafted by the Republicans as a 2012 vice presidential candidate.
But shifting Petraeus out of Afghanistan raises questions about the future of the nearly decade-old war there. Some analysts fear his departure could derail momentum and undermine efforts to improve U.S. ties with Pakistan.
Seeking to show continuity, Obama also nominated trouble-shooting diplomat Ryan Crocker, who has served as ambassador to Iraq, Pakistan, Syria, Kuwait and Lebanon, as the U.S. ambassador to Afghanistan. Lieutenant General John Allen, deputy commander of U.S. Central Command, was named to succeed Petraeus as head of the Afghan war effort.
(Additional reporting by Arshad Mohammed, Steve Holland and Alister Bull)
Editing by Paul Simao