"Our view is that the carriers, because of their presence, because of the power they represent, are a very important part of our ability to maintain power projection both in the Pacific and in the Middle East," he said.
Obama has said he hopes to further reduce the size of the U.S. nuclear arsenal, but Panetta is expected to make clear that the basic structure — a "triad" of land, sea and air nuclear forces — will be maintained. The Pentagon may find some savings by stretching out planned modernization programs.
The defense budget is being reshaped in the midst of a presidential contest in which Obama seeks to portray himself as a forward-looking commander in chief focusing on new security threats. Republicans want to cast him as weak on defense.
Obama has highlighted his national security successes — the killing of Osama bin Laden, the death of senior al-Qaida leaders and the demise of Libya's Moammar Gadhafi — to counter Republican criticism. He also has emphasized the completion of the U.S. troop withdrawal from Iraq and the start of a drawdown in Afghanistan as turning points that offer new opportunities to scale back defense spending.
But several congressional Republicans see a political opening in challenging the reductions in projected military spending that the GOP and Obama agreed to last summer as part of a deal to raise the nation's borrowing authority. They've echoed Obama's potential presidential rivals Mitt Romney, Newt Gingrich and Rick Santorum, who plead for fiscal austerity but contend that sizable cuts would gut the military.
The defense budget this year is nearly $671 billion, including a base budget of $553 billion and $118 billion in war costs. Panetta is expected to announce on Wednesday that the administration's request for 2013 will drop to about $525 billion for the base budget. That is still far higher than the $480 billion base budget for the Pentagon in 2008, President George W. Bush's final year in office.
The administration's projected defense cuts would total nearly $490 billion over 10 years. If Congress fails to agree on other reductions in federal spending this year, the defense hit could double under automatic cuts that would take effect in January 2013.
Several Republicans argue that even the initial cuts totaling nearly $490 billion would "hollow" the military and costs tens of thousands of jobs nationwide, adding to an 8.5 percent unemployment rate that they already blame on the president's economic policies.
"While Secretary Panetta has conceded that our nation is now accepting more risk as a result of the budgetary vise squeezing the Pentagon, it remains unclear exactly what risks our nation is assuming," Rep. Randy Forbes, R-Va., a House Armed Services Committee member, said this week.
Associated Press writers Kimberly Dozier and Lolita C. Baldor contributed to this report.
Robert Burns can be reached on Twitter at http://www.twitter.com/robertburnsAP