With Afghan units in the lead, U.S. troops will still be directly involved in combat for months, the official said. American special forces also will remain in far flung outposts partnering with Afghan units.

A new general in charge

Dunford will oversee the final two years of the war and the withdrawal of nearly all troops.

At a change-of-command ceremony in Kabul on Sunday, Dunford remarked on the job ahead.

"Today is not about change, it's about continuity," he said, alongside Allen and other senior NATO and Afghan officials.

"I'll endeavor to continue the momentum of the campaign and support the people of Afghanistan as they seize the opportunity for a brighter future."

Dunford has a reputation among Marines as a thoughtful, calm leader, with more than 22 months under his belt of commanding troops in Iraq.

These changes come amid debate about impending budget cuts that some say would have grave consequences for the military unless Congress acts to avert them by the start of next month.

Sequestration is a series of automatic, across-the-board cuts to government agencies, totaling $1.2 trillion over 10 years. The cuts would be split 50-50 between defense and domestic discretionary spending.

More than $500 billion would be cut from the Defense Department and other national security agencies, with the rest coming from domestic programs, like national parks, federal courts, the FBI, food inspections and housing aid.

Outgoing Defense Secretary Leon Panetta has been a harsh critic of the cuts.

"For those of you who have ever seen 'Blazing Saddles,'" he said in a recent speech at Georgetown University, there "is the scene of the sheriff putting the gun to his head in order to establish law and order. That is sequestration."