Even before taking over as chairman of the Joint Chiefs of Staff, the highest military office in the land, Army Gen. Martin Dempsey made one thing clear. He differs with his predecessor on one of the most important issues of the day: the threat posed to national security by a growing national debt.

Dempsey was to be sworn in Friday as successor to Navy Adm. Mike Mullen, who is retiring today.

At his Senate confirmation hearing in July, Dempsey was asked whether he agrees with Mullen's oft-repeated assertion that the debt crisis is the single biggest threat to American national security.

"I don't agree exactly with that," Dempsey said.

In his view, developed in the course of a 37-year career that includes two tours of command in Iraq and one in Saudi Arabia, American global power and influence are derived from three strengths: military, diplomatic and economic.

"You can't pick or choose," he said; none of the three is paramount.

It's too early to know how much change Dempsey will foster in his role as the top U.S. military officer, but it's certain that pressures to cut the defense budget and what that implies for the military and for American foreign policy will be a dominant issue from Day One of his tenure.

So while he sees the debt problem as highly important, Dempsey believes the United States cannot be successful in managing its national security and international affairs without asserting influence through a combination of a powerful military, an effective diplomatic corps and a sound economy.

His will be among the key voices in recommending how to cut hundreds of billions of dollars from the defense budget over the coming decade.

By law, the chairman of the Joint Chiefs serves as the senior military adviser to the president, the president's National Security Council and the secretary of defense. But the chairman is not directly in the chain of command that extends from the president to the secretary of defense to commanders in the field. He is the public face of the U.S. military and weighs in on major policy decisions but is not actually in charge of any troops.

Dempsey is the first Army general to hold the job since Hugh Shelton retired in 2001.

One of the legacies of Mullen's four years as chairman was his less-than-successful effort to persuade Pakistan's military chief, Gen. Ashfaq Pervez Kayani, to do more to contain and disable violent extremist groups like al-Qaida and the Haqqani network that use Pakistan as a haven.

In the final week of his tenure, Mullen made his biggest headline by telling a Senate committee that the Haqqanis are a "veritable arm" of Pakistan's intelligence service and by asserting that Pakistani intelligence supported and facilitated a string of Haqqani attacks on Americans in Afghanistan. His statement infuriated the Pakistan government and arguably set back, at least temporarily, an already frayed U.S.-Pakistani relationship.

Dempsey's views on Pakistan's importance to success in Afghanistan appear similar to Mullen's, although he has been less specific about the role of the Haqqanis.

In his July testimony, he said it has never been clear to him why the Pakistani government goes after some extremist groups but not others. He said that as Joint Chiefs chairman he would work with the Pakistanis to improve border security.

Like many who rise to the highest ranks of the U.S. military, Dempsey is not known for his public outspokenness. He took over as Army chief of staff in April. Before that he commanded the Army's Training and Doctrine Command, and he previously served for several months as acting commander of U.S. Central Command with responsibility for all U.S. military operations and relations in the greater Middle East.

He graduated from the U.S. Military Academy at West Point in 1974.

Dempsey's swearing-in completes the transition of President Barack Obama's senior national security team, which included Leon Panetta taking over for Robert Gates as defense secretary on July 1, followed by Marine Gen. John Allen's arrival in Kabul as the new commander of U.S. and NATO forces, Gen. David Petraeus' retirement from the Army to become CIA director and Gen. Raymond Odierno replacing Dempsey as Army chief of staff.

Mullen, who served two two-year terms as Joint Chiefs chairman, is retiring. He has served 43 years in uniform.

In his confirmation hearing testimony in July, Dempsey was not explicitly comparing and contrasting his views with those of Mullen. But in addition to stating a different view on the issue of debt and national security, he echoed Mullen on the matter of defending against cyber threats.

Mullen said several times in his final days in office that cyber attacks are one of just two threats to the continued existence of the nation. The other, he said, is Russian nuclear weapons, and he said that threat is well contained by arms control agreements, including the New START treaty of 2010.

And like Mullen, Dempsey acknowledged that he is not particularly well versed on the subject of cyber warfare.

"I'll confess at the start that my thinking on this is nascent, at best," Dempsey told the Senate Armed Services Committee. He added that he had been advised that cyber war was likely to be one of several issues that define his tenure.

He did not mention what he expects will be the other defining issues, but almost certainly they include winding down the wars in Afghanistan and Iraq and reorienting U.S. forces for the post-war period.