U.S. President Barack Obama plans to nominate CIA director Leon Panetta to succeed Robert Gates as the new defense secretary, media reported Wednesday.

Meanwhile, the commander of U.S. forces in Afghanistan, David Petraeus, will be named to head the CIA and Lt. Gen John Allen will be Petraeus' successor, CNN, ABC News and other media reported, citing anonymous sources.

This would be the most extensive shake-up of Obama's national security team. Also on the list is veteran diplomat Ryan Crocker, who will replace Karl Eikenberry as the next U.S. ambassador to Afghanistan, according to the reports.

Obama was expected to make a formal announcement Thursday. The nominations have to be approved by the Senate.

Panetta, who turns 73 in June, became the CIA director in February 2009. He was chief of staff to President Bill Clinton between 1994 and 1997. The California Democrat served in the House of Representatives from 1977 to 1993.

Gates, a Republican who was appointed by former President George W. Bush, announced last August that he would step down this year.