Mr. Panetta will outline the strategy guiding his spending plans at a news conference this week, and the specific cuts — for now, the Pentagon has prepared about $260 billion in cuts for the next five years — will be detailed in the president’s annual budget submission to Congress, where they will be debated and almost certainly amended before approval. Although the proposals look to budget cuts over a decade, any future president can decide to propose an alternative spending plan to Congress.

The looming cuts inevitably force decisions on the scope and future of the American military. If, say, the Pentagon saves $7 billion over a decade by reducing the number of aircraft carriers to 10 from 11, would there be sufficient forces in the Pacific to counter an increasingly bold China? If the Pentagon saves nearly $150 billion in the next 10 years by shrinking the Army to, say, 483,000 troops from 570,000, would America be prepared for a grinding, lengthy ground war in Asia?

What about saving more than $100 billion in health care cutbacks for working-age military retirees? Would that break a promise to those who risked their lives for the country?

The calculations exclude the costs of the wars in Iraq and Afghanistan, which will go down over the next decade. Even after the winding down of the wars and the potential $1 trillion in cuts over the next decade, the Pentagon’s annual budget, now $530 billion, would shrink to $472 billion in 2013, or about the size of the budget in 2007.

It is also important to remember that Mr. Panetta, a former White House budget chief, understands budget politics like few other defense secretaries. When he sent a dire letter to Capitol Hill late last year that held out the prospect of huge reductions in some of Congress’s favorite weapons programs, analysts saw it as a classic tactic to rouse the Hill to his side.

They noted that Mr. Panetta did not cite the $100 billion that the previous defense secretary, Robert M. Gates, said could be saved by reducing the number of contractors, cutting overhead, consolidating technology and limiting spending in the executive offices of the Pentagon.