Washington - It has been an unlikely Washington feud, pitting a determined Sen. Dianne Feinstein, the implacable chairman of the Senate intelligence committee and long regarded as a supporter of the CIA, against the agency's equally stubborn director, John Brennan.

The culmination of the battle is near, with a vote scheduled Thursday by the Senate committee to release a summary of its 6,300-page report on CIA interrogation practices. The report examines in damning detail one of the darkest chapters in modern American history, in which the agency harshly interrogated al-Qaeda suspects to obtain information.

Feinstein wanted a report so tough that it would "ensure that an un-American, brutal program of detention and interrogation will never again be considered or permitted," as she put it. Feinstein's campaign has advanced that goal, and for this, the country should be grateful. But the investigation process has also badly frayed the mutual trust between Congress and the CIA, because of blinkered actions by both Feinstein and Brennan.

The Senate report includes gruesome new details about interrogation practices in the first year after Sept. 11, 2001, before the CIA's program was formally established with the misplaced approval of President George W. Bush's Justice Department. These details - recounting filthy conditions and vicious interrogation techniques - will shock the conscience in the same way that the Abu Ghraib and waterboarding revelations did.

This is the necessary, curative part of the report. Brennan said in a letter to CIA employees last month that while the agency has "taken corrective measures to prevent such mistakes from happening again," he also wants to make sure "any historical account ... is balanced and accurate." It's the issue of what constitutes balance regarding the inflammatory issue of torture where Brennan and Feinstein have tangled.

The heart of the dispute isn't whether torture is immoral - nobody would argue that question today - but whether it was ever effective. Feinstein's investigators gathered 20 cases where CIA documents most frequently cited information gained from interrogation; the investigators scoured intelligence reports and argued that in each case the information could have been obtained without brutal methods.

The CIA critiqued the 20 cases, pointing out what it claimed were serious errors. The Senate staffers re-crafted the document, fixing mistakes but maintaining the claim that the same intelligence could have been gleaned without torture. The CIA rewrote its rebuttal, continuing its dissent that, even with perfect hindsight, the record was ambiguous.