WASHINGTON — CIA officers subjected some terrorism suspects the agency held after the Sept. 11 attacks to interrogation methods that were not approved by either the Justice Department or their headquarters and illegally detained 26 of the 119 in CIA custody, the Senate Intelligence Committee has concluded in its still-secret report, McClatchy has learned.

The spy agency program’s reliance on brutal techniques — more abusive than previously known — and its failure to gather valuable information from detainees harmed U.S. credibility, according to the committee’s findings in its scathing 6,300-page report on the CIA’s interrogation and detention program.

The agency also repeatedly misled the Justice Department while thwarting congressional and White House efforts to oversee the secret and now-defunct program, McClatchy has learned.

In all, the committee came to 20 conclusions about the CIA’s interrogation tactics after spending six years and $40 million evaluating the program, which began during the Bush administration.

Unlimited Digital Access. $1 for 4 weeks.

The committee voted 11-3 Thursday to declassify an executive summary and conclusions. Despite the bipartisan vote, Republicans and Democrats were at odds over the report’s value, and the three dissenters are Republicans: Sens. Marco Rubio of Florida, Dan Coats of Indiana and Jim Risch of Idaho.

“Too much time, energy and too many resources have been spent investigating a CIA program that ended more than six years ago,” Coats said.

The CIA has rejected some of the findings and has written a still-secret rebuttal.

Sen. Dianne Feinstein, D-Calif., who chairs the committee, maintained that the eventual release of the summary and findings will show “that this nation admits its errors, as painful as they may be, and seeks to learn from them.”

She called the findings shocking, adding: “The report exposes brutality that stands in stark contrast to our values as a nation. It chronicles a stain on our history that must never again be allowed to happen.”

The next step is President Obama’s approval. Obama, who opposed the CIA program as a presidential candidate and discontinued it once he took office in 2009, has said he wants the findings of the report to be made public.

The finding that 26 detainees were held without legal authorization and the confirmation that the CIA in some cases went beyond the techniques approved by the Justice Department might fuel legal challenges.

Sen. Saxby Chambliss of Georgia, the committee’s top Republican, who said he had voted to declassify, was highly critical of the report, however.

He said: It’s “a waste of time,” adding: “There is absolutely concrete evidence that has been gleaned from the individuals who have been interrogated in this program that led not only to (Osama) bin Laden’s takedown but to the interruption and disruption of other terrorist plots over the years.” The Senate panel concluded that the techniques were ineffective.

Material from The New York Times is included in this report.