By Phil Stewart and Adam Entous
WASHINGTON (Reuters) - U.S. General David Petraeus faces a confirmation hearing in the Senate on Tuesday expected to expose growing doubts about the U.S. effort in Afghanistan but broad support for the four-star general chosen to lead it.
One of the U.S. military's biggest stars, Petraeus is widely credited with helping turn the tide in Iraq. President Barack Obama hopes he can do the same with the unpopular, nine-year-old war in Afghanistan.
Petraeus, 57, would replace General Stanley McChrystal, who was fired by Obama last week over comments made by him and his aides belittling the president and his aides and announced his retirement on Monday.
It was the biggest military shake-up of his presidency, and the second time the top Afghan commander was fired since Obama took office last year.
"This is Obama's last chance," Arturo Munoz, a security analyst at the RAND Corporation, said of Petraeus.
If the general who helped pull Iraq back from the brink and oversaw development of the book on counter-insurgency strategy cannot win the war in Afghanistan, maybe no one can, Munoz added.
Carl Levin, chairman of the Senate Armed Services Committee to which Petraeus will testify, cautioned reporters a day ahead of the confirmation hearing that support for the war among Obama's Democrats was starting to erode.
"On the Democratic side, there's I would say solid support but there's also the beginnings of some fraying of that support -- and that's true in the base, as well as in the Congress," he told reporters.
He aimed to press Petraeus to increase the number of Afghan forces who are taking part in a campaign to secure the Taliban's spiritual home of Kandahar, an operation seen as the linchpin of Obama's war strategy.
After a slower-than-expected roll-out, that operation is expected to get fully under way in September and its perceived success or failure could affect Obama's Democrats at the ballot box in November congressional elections.
STRUGGLING CAMPAIGN
The Afghan job is technically a step-down for Petraeus, who used to be McChrystal's boss.
The Army general is widely respected by Republicans and Democrats, and few expect his nomination to be held up. Obama has called for his confirmation before the July 4 holiday.
"I think the hearing is going to be warm and very positive regarding Petraeus himself ... But in regard to the counter-insurgency strategy, no. That's going to be different," said Munoz. "There are going to be a lot of hard questions."
Perceptions of a struggling U.S. campaign have been fuelled by a stronger-than-expected Taliban resistance in the southern district of Marjah -- meant to be a showcase of U.S. strategy -- and the slow start to the offensive in Kandahar.
In a sign of growing tensions, a key Democratic lawmaker in the House of Representatives said she was cutting billions of dollars in aid to Afghanistan from spending legislation because of reports of corruption and donor aid being flown out of the country.
Representative Nita Lowey, who heads the House appropriations subcommittee on foreign aid, vowed not to spend "one more dime" on aid to Afghanistan until she can be sure it is not being abused.
Petraeus, who briefly fainted the last time he appeared before the Senate committee -- he blamed dehydration -- is also expected to face tough questions from opposition Republicans critical of Obama's plan to start withdrawing U.S. troops in July 2011.
Senator John McCain, the ranking Republican on the committee, has criticized the timeline and said it sent a signal to Afghans that the United States and its allies were preparing to wrap up the war regardless of the outcome.
Levin said the July 2011 date was crucial to Americans wary of making an open-ended commitment to the Afghan conflict.
"That date being set I think was critically important in terms of maintaining support of the American people (for) a war that has gone on so long," Levin said.
Ramping up Afghan security forces is a precondition for any eventual pullout by American forces. But a report on Monday by the U.S. special inspector general for Afghanistan reconstruction underscored the difficulty of training Afghan troops to take over the country's security.
"We don't really know at this point in time what the capability of the Afghanistan security forces really is," chief inspector Arnold Fields told reporters, highlighting problems of drug abuse and corruption.
(Additional reporting by Susan Cornwell; editing by David Alexander and Mohammad Zargham)
