When it comes to national security issues in 2012, the person who faces the toughest choices is Defense Secretary Leon E. Panetta.

Look at what’s on his plate: the Pentagon’s budget crunch, the war in Afghanistan, the postwar period in Iraq, Iran’s nuclear ambitions, Israeli issues, U.S.-Pakistan relations, China’s growing military and the biggest challenge of all — Congress.

Hovering over him like a cloud is the presidential campaign. A chorus of Republican candidates, as Mitt Romney already has done, will almost certainly take issue with the Obama administration’s defense policies and spending levels. While the economy will be central to the campaign debate, defense will be a close second.

The budget crunch goes far beyond numbers. This week, the Pentagon will produce a revised defense strategy that will provide the basis for the fiscal 2013 Defense Department budget. The numbers themselves will come later this month as part of President Obama’s budget and will reflect the second year of a 10-year plan to cut $489 billion in defense spending, made in response to August’s Budget Control Act.

It remains to be seen what further defense reductions will be made as Congress wrestles with the “sequestration” requirement in the August statute — across-the-board budget cuts of more than $1 trillion over 10 years, half of which are to come from national security spending. These cuts were triggered by the failure last fall of the congressional “supercommittee” to come up with a deficit-reduction plan.

U.S. Secretary of Defense Leon Panetta has a lot on his plate: the Pentagon’s budget crunch, the war in Afghanistan, the postwar period in Iraq, Iran’s nuclear ambitions, Israeli issues, U.S.-Pakistan relations, China’s growing military and the biggest challenge of all — Congress (Omar Sobhani/REUTERS)

In a Nov. 14 letter to Sens. John McCain (R-Ariz.) and Lindsey O. Graham (R-S.C.), Panetta wrote that the Budget Control Act cuts “are difficult and will require us to take some risks, but they are manageable.” Further cuts under sequestration, he said, “would tie [the Defense Department’s] hands.” For instance, he said that across-the-board reductions would have to be applied equally to major construction programs, rendering “most of our ship and construction projects ‘unexecutable’ — you cannot buy three quarters of a ship or a building — and seriously damage our modernization efforts.”

Panetta has proposed that, if additional cuts are required, the Pentagon be allowed to pick and choose where they are made and not have to apply them across the board.

To reach the initial $489 billion in cuts, Panetta will have to defend before Congress the expected reductions in personnel for fiscal 2013, as well as the scaling back or ending of some weapons programs. All of these have their constituents inside and outside government — and especially on Capitol Hill.

How many F-35s do you buy; should you choose manned or unmanned weapons systems; how many nuclear supercarriers do you need; do you modernize all three legs of the nuclear triad — strategic bombers, land-based intercontinental ballistic missiles and strategic submarines? While dealing with these questions, Panetta must also protect money for operations, maintenance, and research and development, the favorite areas for congressional budget cutters.

He must also determine the size of reductions in military personnel, which smaller weapons programs will be cut or ended, and how much should be spent on the future through research and development.

Sometime this year, there must be decisions on how to downsize in Afghanistan and what arrangements can be made to keep U.S. forces there after 2014, whether to send military trainers back to Iraq, and how to respond if Congress authorizes dispatching Special Forces to Nigeria to assist in fighting a terrorist group, as it did when U.S. troops were sent to help battle the Lord’s Resistance Army in central Africa.

Then there are the military issues that have election implications. Are personnel coming home from Iraq and Afghanistan getting enough help; what’s being done to reduce military suicides; are boards needed to determine which officers and senior enlisted troops should be retired as overall numbers go down; how do you monitor the end of “don’t ask, don’t tell” and the new legislation dealing with sexual abuse and rape in the military? Who will be on the promised commission to look into changes in the military retirement system and perhaps the Pentagon’s health system?

These are all complicated issues, more often handled through small steps and compromise than through simplistic, black-and-white pronouncements — like campaign rhetoric.

Speaking on Oct. 6, Romney said that he wanted Pentagon core spending to rise to 4 percent of gross domestic product and that he would increase active-duty personnel by about 100,000. In a speech the next day at the Citadel, he said he would “reverse the hollowing of our Navy and . . . increase the shipbuilding rate from nine per year to 15.” He also repeated a pledge that has Republican roots going back to the Nixon administration: “I will begin reversing Obama-era cuts to national missile defense and prioritize the full deployment of a multilayered national ballistic missile defense system.”

During the Nov. 22 Republican presidential debate, Romney said the Obama administration, in response to the Budget Control Act, halted production of the F-22 stealth fighter, delayed aircraft carriers and said new long-range Air Force bombers would not be built. These steps and others, Romney said, are “cutting the capacity of America to defend itself.”

Panetta did not step forward to challenge these remarks, though others have noted, for example, that the decisions to limit F-22 production and slow carrier production were made by then-Secretary Robert M. Gates before the Budget Control Act passed, while plans for the strategic bomber are still going ahead.

When the presidential campaign becomes a two-person race in the fall, and the GOP candidate, his supporters or political action committees make similar charges against the Obama defense program, the feisty, outspoken politician inside Panetta may not be so controlled. “I am not sure Panetta will stay totally out of the fray,” said a person who knows the defense secretary well.