Although Senate confirmation of Army Gen. David H. Petraeus to become the next head of the U.S. Central Command appears to be all but ensured, continuing tensions over President Bush’s Iraq policy could make his confirmation hearings difficult.

Bush soon will nominate Petraeus, now the commander of multinational forces in Iraq, to lead “Centcom”— the Tampa, Fla.-based organization that oversees U.S. forces across the Middle East and South Asia, Defense Secretary Robert M. Gates announced Wednesday.

Gates said Petraeus is expected to continue serving in Iraq through late summer or early fall. He would be replaced there by Lt. Gen. Raymond Odierno, who served as Petraeus’ deputy in Iraq before being nominated in February to become Army vice chief of staff. Odierno’s nomination as vice chief was withdrawn before the Senate ever voted on it. Bush intends to nominate Lt. Gen. Peter Chiarelli, Gates’ senior military assistant, as Army vice chief of staff.

Petraeus is the architect of the current counterinsurgency strategy in Iraq, which has led to decreased violence over the past year. But because it is unclear when the bulk of U.S. troops can begin to come home from Iraq, the war remains a volatile political issue, and the Petraeus nomination is likely to become the venue for the debate in the weeks ahead.

Senate Majority Leader Harry Reid, D-Nev., made clear that the nominations of Petraeus and Odierno would receive intense scrutiny, at least from Democrats.

“The next Centcom commander and field commander in Iraq will have to help the next president with a number of critically important challenges: making America more secure, restoring America’s power and influence in the world, fixing our costly strategy in Iraq, and articulating a more effective strategy for winning in Afghanistan and defeating al Qaeda in Pakistan,” Reid said.

“The Senate will carefully examine these nominations, and I will be looking for credible assurances of a strong commitment to implementing a more effective national security strategy.”

Petraeus will take over U.S. Central Command from Adm. William J. Fallon, who recently stepped down amid perceptions that he had deviated from the administration’s hard-line approach to Iran and its plan to continue high U.S. troop levels in Iraq. Gates said he hopes the Senate will confirm Petraeus by Memorial Day.

When the Senate takes up the nomination, all three remaining major presidential candidates could get a say on the nomination, assuming they are not diverted by campaigning.

John McCain of Arizona, the presumed GOP presidential nominee, is the ranking Republican on the Armed Services Committee, which will conduct the hearings. Hillary Rodham Clinton, D-N.Y., also serves on Armed Services. Barack Obama, D-Ill., will not have a role until the nomination reaches the Senate floor, when he will have an opportunity to vote on confirmation.

Gates said he has discussed the nomination with McCain, Armed Services Chairman Carl Levin, D-Mich., and John W. Warner of Virginia, the longest-serving Republican on the panel. The secretary said it was likely that the Senate would confirm Petraeus.

“He has clearly been successful in his current assignment, so I don’t anticipate any problems,” Gates said.

McCain endorsed the nomination in a statement Wednesday, calling Petraeus “one of the great generals in American history.”

Petraeus told the Senate Armed Services Committee on April 8 that he recommended a halt to troop withdrawals for at least 45 days once the “surge” forces, added last year, depart this summer. Bush accepted that recommendation, although many lawmakers in both chambers expressed deep concerns about the open-ended nature of the commitment.

Bush’s decision means the number of U.S. troops in Iraq would level off at about 140,000 in July, down from about 156,000 now. Administration officials will decide after the pause if and when withdrawals might continue.

Petraeus refused to specify how long troop levels might be held at 140,000, saying further withdrawals would depend on the situation on the ground in Iraq.

“When the conditions are met, we will make the recommendations for further reductions,” he said.

Reaction to the nominations of Petraeus and Odierno was mostly positive Wednesday, with some Democratic skepticism about the road ahead in Iraq and Afghanistan.

Minority Leader Mitch McConnell, R-Ky., called the selection of Petraeus to head the Central Command an “inspired and sensible choice” and said he should be confirmed by the Senate.

“Once confirmed, our nation will be fortunate to have General Petraeus guide our strategy to protect American interests in Afghanistan, Pakistan, Iraq and the wider region of the world,” McConnell said.

Several Democrats were decidedly more guarded.

“I have great respect for General Petraeus and the job he has done in Iraq,” said Joseph R. Biden Jr., chairman of the Foreign Relations Committee. “But if confirmed, Gen. Petraeus’ mission will no longer be just Iraq — it will be the entire region, including the Afghanistan-Pakistan border area where those who actually attacked us on 9/11 have regrouped, where our ambassador to Iraq acknowledged to me that al Qaeda is a bigger threat, and where we do not have enough troops because of Iraq. Congress must ensure that Gen. Petraeus does not bring an Iraq bias to his new job, at the expense of America’s broader security needs.”

Ben Nelson of Nebraska, a Democrat on Armed Services, said Petraeus was a “logical” choice to lead the Central Command. But he, too, sounded a cautionary note.

“It will be important that Gen. Petraeus keep Centcom focused on all the threats and missions in the region, including Iraq, Afghanistan, Pakistan and matters in Africa,” Nelson said in a statement.