In an opening message to Defense Department personnel, Panetta acknowledged the fiscal challenges he is inheriting, including an administration request to identify $400 billion in savings from the defense budget over the next 12 years. But Panetta also said that he believes in achieving a balance between disciplined spending and doing what is necessary to protect U.S. forces.

“While tough budget choices will need to be made, I do not believe in the false choice between fiscal discipline and a strong national defense,” he said, virtually echoing remarks by his predecessor, Robert. M. Gates. “We will all work together to achieve both.”

Panetta was sworn in as secretary at a private ceremony shortly before 9 a.m. Gates began squeezing some reductions out of the Pentagon budget before his departure,outlining ways to save $178 billion over the next five years. But achieving further reductions — after a decade of almost unchecked spending -- is expected to be one of the biggest challenges for Panetta.

While Gates largely backed Obama’s calls for deeper cuts, he warned that those reductions must be executed with an eye toward strategy and could not be carried out simply as a “math exercise.”

On Thursday, a new report from the Congressional Budget Office projected that higher costs for weapons systems and health care will increase the Pentagon budget by $40 billion over the next five years.

In an op-ed in the Wall Street Journal on Friday, former defense secretary Donald Rumsfeld warned that it would be a “grievous mistake” for Panetta to accede to President Obama’s proposal to carve $400 billion from the defense budget.

“While there are substantial savings to be found in the defense budget, hundreds of billions cannot be cut without impairing our security,” Rumsfeld said. “Mr. Gates has said that he's already made the ‘easy’ cuts, yet there are serious questions whether some of them ... leave America ill-prepared for a conventional conflict and erode the strong deterrent necessary to prevent it.”

Rumsfeld’s tenure at the Pentagon was marked by big increase in the defense budget and few cuts, so much so that Gates described the hundreds of billions of dollars in cuts that he made in 2009 as “no-brainers.”

YOUR TAKE: What would you cut?

Tweet What would you cut from the Pentagon budget to pay down the federal deficit? Defense spending mostly consists of three bins -- war costs (current operations), pay and benefits, and weapons systems. Where would you start? Are there any specific programs that you would cut?

Here are a few responses to the #DefenseCuts questions...

@checkpointwash Funds for constructing more bases, many/most arms procurement programs #DefenseCutsless than a minute ago via web Favorite Retweet ReplyYes I Care

@checkpointwash Cut out useless equipment that even the generals say we don’t need. #DefenseCuts #MilitaryIndustrialComplex #WhatEducation?less than a minute ago via web Favorite Retweet ReplyAnthony Colucci