WASHINGTON — After President-elect Donald J. Trump promised to “drain the swamp” that he sees in the nation’s capital, his millions of supporters are expecting vast changes in the sprawling federal bureaucracy, and conservative activists are drooling at the chance to remake, resize or reduce the reach of government.

Mr. Trump repeatedly told voters during the campaign that he would shut down the Environmental Protection Agency and repeal the Affordable Care Act. He said the Education Department is “massive, and it can be largely eliminated.” He has made the federal work force of 2.8 million employees a target, declaring that “you have tremendous waste, fraud, and abuse.”

But the one-time real estate mogul has largely avoided specifics about cuts he might make, and much of his agenda imagines changes that would require huge increases in federal spending: tripling the number of border patrol agents; supplying the military with more warships and fighter jets; increasing spending on infrastructure; undertaking new efforts to confront cyberterrorism; and aggressively working to remake trade policies.

Whatever change he envisions will likely be vastly more difficult to enact than his army of supporters believe. Veterans of Washington’s many fights over policy warn that the city is full of ingrained bureaucracies, each of which has entrenched support on Capitol Hill. And while Mr. Trump will have some executive authority, legal, practical and political limitations will constrain his efforts.