The US Senate unanimously confirmed Leon Panetta as US defense secretary on Tuesday, hailing his successes as the chief of the CIA just as major challenges await him in Afghanistan and Libya.

All 100 members of the Senate approved the nomination of Panetta, a rare show of unanimous support for a federal government official.

The incoming defense chief will have to oversee a troubled war in Afghanistan, the withdrawal of the remaining US troops in Iraq, and US participation in the NATO-led Libya campaign.

Lawmakers hailed his role in tracking down and eliminating Osama bin Laden, who was killed in a dramatic US commando raid last month deep in Pakistan.

"The nomination of Leon Panetta to be secretary of defense is a wise and solid one," said Senator Carl Levin, the Democratic chairman of the Senate Armed Services Committee.

John McCain, the top Republican on Levin's panel, said that Panetta, as CIA director, "has demonstrated he possesses the experience and ability to ensure that we achieve our objectives in the three conflicts in which US forces are now engaged: Iraq, Afghanistan and Libya".

Panetta, who began his political career as a lawmaker in Congress, will be the first Democrat to hold the top defense job since William Perry in 1997.

In a break with Robert Gates, the outgoing Pentagon chief, Panetta has said he supports withdrawing a significant number of troops from Afghanistan next month.

Obama was scheduled to announce on Wednesday his plans to withdraw troops from Afghanistan as the military works to put Afghans in charge of their own security by 2014 and bring to a close what is now an almost decade-long war.

A senior defense official said on condition of anonymity that the president is "likely" to order the withdrawal of about 10,000 troops from Afghanistan this year. Half are to leave this summer and half by the end of 2011.

Another 20,000 troops, part of a 30,000 strong-forces, sent out in December 2009, is to be withdrawn by the end of next year.

Panetta, on track to replace Gates on July 1, will be in charge of managing the withdrawals and other operations in Afghanistan, where the United States now maintains 99,000 troops.

He would also oversee the US military intervention in Libya against the regime of longtime ruler Muammar Gadhafi. That operation began in March.