President Barack Obama is expected to nominate intelligence director Leon Panetta to succeed Robert Gates as defense secretary when he resigns this summer. General David Petraeus, currently the commander of American and ISAF forces in Afghanistan, would replace Panetta as head of the CIA.

Panetta, a former congressman and White House chief of staff under Bill Clinton, became director of the Central Intelligence Agency in February 2009. As a surprise candidate for the position, Panetta managed to overcome opposition from senior lawmakers who questioned his lack of intelligence experience. At age 72, he would be the oldest person to take the helm of the Pentagon.

His experience working with a Republican Congress during the Clinton years could serve him well as the opposition controls the House of Representatives and is deeply skeptical of cutting defense spending as the president has suggested.

Gates, who replaced Donald Rumsfeld at the Defense Department during the Bush Administration, never planned to sit out the full term of Barack Obama’s first cabinet.

During his tenure, Gates attempted to reduce the growth of defense spending, stating, more than a year ago, that if his department couldn’t “figure out a way to defend the United States on half a trillion dollars a year, then our problems are much bigger than anything that can be cured by buying a few more ships and planes.” Congressmen have nevertheless hesitated to scrap expensive defense projects, especially if they are developed in their districts or states.

In what was something of a farewell address last March, Gates laid out his vision on the future of the American military, professing that “in the competition for tight defense dollars within and between the services,” the focus should be on preparing for naval and air engagements.

The strategic rationale for swift moving expeditionary forces, be they army or marines, airborne infantry or special operations, is self-evident given the likelihood of counterterrorism, rapid reaction, disaster response or stability or security force assistance missions.

“But,” Gates added, “as the prospects for another head on clash of large mechanized land armies seem less likely, the army will be increasingly challenged to justify the number, size and cost of its heavy formations to those in the leadership of the Pentagon, and on both ends of Pennsylvania Avenue, who ultimately make policy and set budgets.”

At the same time, Gates acknowledges that the need for a counterinsurgency capacity remained, “to prevent festering problems from growing into full-blown crises which require costly — and controversial — large-scale American military intervention.” It is why he worked to better equip the US Army and Marine Corps to make them more agile and flexible, sometimes at the expense of big and expensive air force and navy pet projects.

As the United States remain involved in two ground wars in Asia and the enforcement of a no-fly zone over Libya, Panetta, a Democrat, will be hard pressed to convince conservative lawmakers to make Gates’ vision for a smaller and cheaper army come true. Donald Rumsfeld tried to transform the military into a leaner fighting force but even with his own party in the majority for six years, he found it difficult to implement big reforms.

The need for spending restraint is certainly real. In order to mend a record $1.6 trillion deficit, Republicans have proposed controversial reforms to health support programs but no defense cuts. President Obama favors a “balanced” approach that includes tax increases and modest savings in the national-security budget. “We need to not only eliminate waste and improve efficiency and effectiveness,” he said earlier this month, “but we’re going to have to conduct a fundamental review of America’s missions, capabilities and our role in a changing world.”

Gates identified some $400 billion in unnecessary defense spending but warned last year that “tough economic times or the winding down of a military campaign” should not lead to “steep and unwise reductions in defense.” It will be up to Panetta to argue that steeper spending reductions aren’t in fact unwise at all.