U.S. Army General Martin Dempsey assumes his post Friday as President Barack Obama?s choice for the new chairman of the Joint Chiefs of Staff.  .

General Martin Dempsey comes from the trenches, a veteran of two wars in Iraq and one in Afghanistan.

He takes over as the nations? top military officer at a time when the Defense Department's budget faces cuts of $450 billion  or more, and troop drawdowns in Iraq and Afghanistan.   

On leaving his previous brief post as army chief this month, he laid out his vision.

"There are some words and phrases that will describe our army in the future, but decline is not one of them," said General Dempsey. "Smaller?  Probably.  Different?  As a learning organization, I hope so.  The best in the world, you better believe it.  Doing what?s right for the country, absolutely. "

Dempsey has a reputation as an effective and respected commander, an intellectual and a strategist -- an officer who brings the perspective of the battlefield to Washington.

Analysts say that unique view is critical as the U.S. military shifts from a period of consistent war over the past decade to a new era of necessary adjustment. Clark Murdock is with the Center for Strategic and International Studies.

"I think his experience as a former commander - and he has held many different levels of command within the army - and the army has been the most stressed of the services, he knows the problem up close and personal of what?s involved in maintaining the quality of the force," he said.

Another big challenge that awaits Dempsey is managing complicated relations with Pakistan, a U.S. ally in the war in Afghanistan and against terrorism.

Dempsey?s predecessor, Admiral Mike Mullen recently accused Pakistan's intelligence service of supporting Afghan extremists who have targeted Americans.  

"The Haqqani network, for one, acts, as a veritable arm of Pakistan?s internal services intelligence agency," said Admiral Mullen.

Aside from being what a Pentagon colleague describes as a commander?s commander, General Dempsey known for singing at parties, and - most notably - his interpretations of the famous songs of the late Italian-American singer Frank Sinatra.

Dempsey?s renditions of the song New York, New York  have drawn the attention of Defense Secretary Leon Panetta.

"He?s a passionate student of history, of the military, and they also tell me of Frank Sinatra," said Panetta. "They tell me there are videos floating around the Internet of Marty belting out his favorite Sinatra tunes. I assume he?s trying to be an aspiring member of the rat pack. But Marty, I hate to tell you - as someone of Italian heritage - you?d better stick to your day job."

In the new job, Dempsey will have the serious tasks of defeating Afghan insurgents, bringing home the troops, streamlining the military, and do it all on a tighter budget.