WASHINGTON  A shift in authority has given military officials at the White House a bigger operational role in creating a backup government if the nation’s capital were “decapitated” by a terrorist attack or other calamity, according to current and former officials involved in the decision.

The move, which was made in the closing weeks of the administration of President George W. Bush, came after months of heated internal debate about the balance of power and the role of the military in a time of crisis, participants said. Officials said the Obama administration had left the plan essentially intact.

Under the revamped structure, the White House Military Office, which reports to the office of the White House chief of staff, has assumed a more central role in setting up a temporary “shadow government” in a crisis.

And the office, a 2,300-person outfit best known for flying Air Force One, has taken on added responsibilities as the lead agent in shepherding government leaders to a secure site at Mount Weather in rural Virginia, keeping classified lists of successors and maintaining computer systems, among other operational duties. Many of these types of tasks were previously handled by civilians at other agencies, led by the Federal Emergency Management Agency.