President Barack Obama on Thursday formally nominated Leon Panetta as his new secretary of defense and David Petraeus, who commands the international force in Afghanistan, as Panetta's successor at the CIA.

Obama had first said he planned to nominate Panetta and Petraeus on April 28, just days before US commandos entered Pakistan and shot and killed Al-Qaeda chief Osama bin Laden.

The US Senate must confirm both men, but neither is expected to encounter any serious opposition there.

The White House hopes that Panetta, whose mission would include cutting spending at the Defense Department, would be able to move into the job on June 30, the day current Defense chief Robert Gates is set to leave.

Petraeus will continue to lead the international force in Afghanistan until his successor, General John Allen, takes over in September. Petraeus will retire from the military before moving to the CIA.

The United States began troop withdrawals from Afghanistan this year, making good on a promise by Obama to reduce US troop levels there, although it is not clear how soon or how many additional troops will leave.

A new chairman of the Joint Chiefs of Staff, who is the president's top military adviser, is also expected to be nominated next month. General Martin Dempsey, the current Army chief of staff, is considered Obama's likely choice to replace Admiral Michael Mullen, according to Pentagon officials.