Petraeus has been the prime advocate of Bush's policy of a large troop presence in Iraq. By naming Petraeus to a job that lasts into the next administration, Bush ensures that the new president will confront the military's strongest voice for maintaining a big force in Iraq.
And Petraeus has emerged as a leading critic of Iran's interference in Iraq, making his appointment a signal of heightened U.S. attention to Tehran. His expertise with Iran's military and political leadership will allow him to take a more hands-on approach to dealing with the government.
Defense Secretary Robert M. Gates said Wednesday that Bush would nominate Petraeus to take over as chief of U.S. Central Command, which also oversees Afghanistan and Pakistan.
The job was left vacant in March when Navy Adm. William J. Fallon stepped down abruptly after appearing to criticize U.S. policy in the region, especially in Iran.
At the same time, Gates said, Bush will nominate Army Lt. Gen. Raymond T. Odierno to take over Petraeus' current job as top U.S. commander in Iraq.Odierno had served directly under Petraeus as day-to-day Iraq commander before stepping down in February.
Like Petraeus, Odierno has urged that Pentagon leaders and policymakers approach U.S. troop reductions cautiously to avoid creating gaps in Iraq's fragile security.
Both men must await Senate confirmation. Although confirmation hearings will be confrontational, with Democrats criticizing Bush's war policy, both men are likely to be approved.
Despite the policy disagreements, Petraeus and Odierno command wide respect because of their success in reducing the level of violence in Iraq.
During his time as Iraq commander, Petraeus has grown steadily more critical of Iran's interference in Iraq's politics and of its role in contributing to violence.
When he took command of U.S. forces in Iraq in 2007, Petraeus was surprised at the extent of Iranian meddling, said some who have worked with him.
During recent appearances in Washington, Petraeus highlighted "nefarious activities" by Iran's Quds Force and charged that the unit has armed Iraqi "special groups" that have killed U.S. troops.
"We should all watch Iranian actions closely in the weeks and months ahead, as they will show the kind of relationship Iran wishes to have with its neighbor," Petraeus told Congress.
But Petraeus also has displayed a keen understanding of the current Iranian government, and many said he would approach Tehran with reserve.
"You will find a very pragmatic general," said Frederick W. Kagan, a scholar at the American Enterprise Institute who has advised the Bush administration on its war strategy. "The Iranians won't be happy because they are not going to be able to feed him nonsense. But he won't be handing anyone in Washington memos saying, 'It's time to go to war.' "
In his new post, Petraeus will have a chance to solve a problem that, before now, he and others could only complain about.
"The question is not if Iran is unhelpful in Iraq," said P.J. Crowley, a retired Air Force colonel and a fellow at the Center for American Progress. "The question is what to do about it."
Once Bush leaves office, his successor is free to change his policies. On Iraq, the president's most important influence will be through the military officers he installs in command.
Although top officers will not set policy themselves, they will be responsible for assessing the war effort and offering the new president their best advice.
Petraeus is unlikely to color the advice he gives the next president, even if the next commander in chief calls for sharp cutbacks in troop levels, said Conrad Crane, director of the U.S. Army Military History Institute.
"He will give his best advice about what he thinks is the right strategy. He won't shape any recommendations based on the political winds. He will make his recommendations based on the reality on the ground," Crane said
But Petraeus will give that advice in private, Crane said, and if it is rejected, he will seek to carry out the new president's policy.
Military officers like Petraeus and Odierno, he said, are used to changes in administrations.
"They serve the commander in chief. There will not be any problems," said William L. Nash, a retired Army major general. "They will give the next president their best advice, argue their case and then salute when given their orders."
Richard J. Danzig, secretary of the Navy under President Clinton and now an advisor to the presidential campaign of Democrat Barack Obama, praised Petraeus but said the next administration should weigh his advice against that of others.
"Gen. Petraeus is particularly capable, and it would be good for any administration to work with him," Danzig said. "The problem is not that he is valued; it is that the advice of so many other able military leaders has been suppressed or ignored by this administration."
In announcing the nominations Wednesday, Gates noted that all military commanders serve at the pleasure of the president.
"I was just trying to provide some continuity for a new administration, but they always have the opportunity to make a change," Gates said.
Still, military experts consider the act of ousting a top officer unlikely, arguing that such a move would needlessly politicize the job of war commander.
In his new job, Petraeus will have responsibility for overseeing military operations from the Horn of Africa through the Persian Gulf to Pakistan and Afghanistan.
Oversight of the war in Afghanistan is split between the U.S. Central Command and NATO.
Afghanistan will pose an interesting challenge for Petraeus. While U.S. and NATO commanders there have been requesting more troops, any additional U.S. forces for Afghanistan would have to come from Iraq.
"The main question is will he be willing to see resources shift from Iraq to Afghanistan?" said Crowley, the retired Air Force colonel, who now advises the presidential campaign of Democrat Hillary Rodham Clinton.
Gates said Wednesday that Petraeus' role in Afghanistan would be somewhat limited.
But historian Crane said that as Centcom commander, Petraeus will have plenty of opportunities to inject new ideas into the Afghanistan fight. Petraeus knows how to work with allied commanders, and his reputation will ensure that people listen to his ideas, Crane said.
"This job will give Gen. Petraeus more of a chance to influence what is going on in Afghanistan," said Crane, a retired Army colonel who helped Petraeus write the Army's 2006 counterinsurgency field manual.
"If you were someone who thought Afghanistan was in need of a fresh approach, you should be excited about Gen. Petraeus' appointment."
Times staff writer Peter Spiegel in Washington contributed to this report.
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