The U.S. must avoid rash decisions to slash the size of the Army in order to rein in the defense budget, the new chief of the Army said Wednesday.

Army Gen. Ray Odierno, who was sworn in during a ceremony at Fort Myer in Arlington, Va., told a packed auditorium of family, friends and fellow soldiers that policymakers must be thoughtful and understand the national security risks as they make difficult fiscal decisions.

"''We must avoid our historical pattern of drawing down too fast and getting too small, especially since our record of predicting the future frankly has not been very good," said Odierno, who has served in the Army for 34 years.

Defense Secretary Leon Panetta noted Odierno's repeated deployments to Iraq, which totaled 50 months, calling him the architect of the so-called surge.

Odierno was second in command to Gen. David Petraeus from late 2006 to early 2008, as U.S. troops poured into Iraq to tamp down the escalating violence. He took over as the top commander in September 2008 and was responsible for the start of the U.S. withdrawal and transfer of security to the Iraqis.

The 1976 West Point graduate replaces Gen. Martin E. Dempsey as Army chief. Dempsey will become chairman of the Joint Chiefs of Staff when Adm. Mike Mullen retires at the end of the month.

Odierno and other top leaders praised Dempsey's meteoric rise through the ranks and credited him with moving the Army to shorter, nine-month deployments, rather than the yearlong tours soldiers have been serving in Iraq and Afghanistan.

But they also joked about his short tenure as chief — which lasted just 149 days before President Barack Obama tapped him for the chairman's post.

"Some might say he just can't hold a job," quipped Odierno. And Army Secretary John McHugh told Dempsey, "Thanks for stopping by."

Later, Dempsey acknowledged that the Army will be smaller in the years to come, but he said officials must find the right balance of people, equipment, training and other services for the soldiers and their families.

"We've got to decide what does the future security environment demand and where will our priorities be," said Dempsey, who will take over as chairman on Oct. 1. "We can't be everything to all people everywhere. We have to prioritize our efforts."

He said there have been no decisions made on how big the Army should be in 2020 or what programs should be on the chopping block.

As for his brief tenure as Army chief, Dempsey, who joined the service 37 years ago, told Odierno he wished that he could have gotten a few more things done for him before leaving.

But Dempsey added that his mantra has always been: "Don't count the days, make the days count."