WASHINGTON — Senators, spies and a president spent years in a pitched battle over how the history is told of one of the most controversial chapters of America’s campaign against terrorism, the detention and interrogation of prisoners in secret C.I.A. jails.

But recent moves by the Trump administration have increased the likelihood that much of what is known about the macabre humiliations that unfolded in those jails around the world will remain hidden from public view.

Congressional officials said on Friday that the administration had begun returning to Congress copies of a 6,700-page Senate report from 2014 about the C.I.A. program. The move raises the possibility that most of the copies could be locked in Senate vaults indefinitely or even destroyed — and increases the risk that future government officials, unable to read the report, will never learn its lessons.

The classified report is the result of a lengthy investigation into the program by Democrats on the Senate Intelligence Committee, telling the story of how — in the years after the Sept. 11, 2001, terrorist attacks — the C.I.A. began capturing terrorism suspects and interrogating them in secret prisons beyond the reach of the American judicial and military legal systems. The central conclusion of the report is that the spy agency’s interrogation methods — including waterboarding, sleep deprivation and other kinds of torture — were far more brutal and less effective than the C.I.A. described to policy makers, Congress and the public.