Washington (CNN) President Barack Obama is expected to announce his pick for the next chairman of the Joint Chiefs of Staff this week, perhaps as soon as Tuesday, a senior U.S. official told CNN.

Several officials say the front runner remains Gen. Joseph Dunford, currently the Commandant of the Marine Corps. The other major contender is General Mark Welsh, Air Force Chief of Staff.

Some officials told CNN it's believed Dunford may have initially declined the job, in favor of staying as head of the Marine Corps, a post he only started last October. Prior to that he served as the head of U.S. and NATO operations in Afghanistan.

But Welsh's nomination could be problematic as well. One congressional official noted that the Air Force has had many run-ins with Congress over the rising costs of its major weapons programs. That could lead to a contentious confirmation process with the Senate Armed Services Committee Chairman, Sen. John McCain, R-Arizona.

Read More