Senator Dianne Feinstein, Democrat of California and chairwoman of the Intelligence Committee, gave few details about the dispute on Tuesday as she left a closed committee hearing on the crisis in Ukraine, but she did confirm that the C.I.A. had begun an internal review. “There is an I.G. investigation,” she said. Asked about the tension between the committee and the spy agency it oversees, Ms. Feinstein said, “Our oversight role will prevail.” The episode is a rare moment of public rancor between the intelligence agencies and Ms. Feinstein’s committee, which has been criticized in some quarters for its muscular defense of many controversial intelligence programs — from the surveillance operations exposed by the former National Security Agency contractor Edward J. Snowden to the Obama administration’s targeted killing program using armed drones.

The Central Intelligence Agency’s attempt to keep secret the details of a defunct detention and interrogation program has escalated a battle between the agency and members of Congress and led to an investigation by the C.I.A.’s internal watchdog into the conduct of agency employees.

The agency’s inspector general began the inquiry partly as a response to complaints from members of Congress that C.I.A. employees were improperly monitoring the work of staff members of the Senate Intelligence Committee, according to government officials with knowledge of the investigation.

The committee has spent several years working on a voluminous report about the detention and interrogation program, and according to one official interviewed in recent days, C.I.A. officers went as far as gaining access to computer networks used by the committee to carry out its investigation.

The events have elevated the protracted battle — which began as a fight over who writes the history of the program, perhaps the most controversial aspect of the American government’s response to the Sept. 11 attacks — into a bitter standoff that in essence is a dispute over the separation of powers and congressional oversight of spy agencies.

The specifics of the inspector general’s investigation are unclear. But several officials interviewed in recent days — all of whom insisted on anonymity, citing a continuing inquiry — said it began after the C.I.A. took what Senator Mark Udall, Democrat of Colorado, on Tuesday called an “unprecedented action” against the committee.

The action, which Mr. Udall did not describe, took place after C.I.A. officials came to suspect that congressional staff members had gained unauthorized access to agency documents during the course of the Intelligence Committee’s years-long investigation into the detention and interrogation program.

It is not known what the agency’s inspector general, David B. Buckley, has found in the investigation or whether Mr. Buckley has referred any cases to the Justice Department for further investigation. Spokesmen for the agency and the Justice Department declined to comment.

Senator Dianne Feinstein, Democrat of California and chairwoman of the Intelligence Committee, gave few details about the dispute on Tuesday as she left a closed committee hearing on the crisis in Ukraine, but she did confirm that the C.I.A. had begun an internal review.

“There is an I.G. investigation,” she said.

Asked about the tension between the committee and the spy agency it oversees, Ms. Feinstein said, “Our oversight role will prevail.”

The episode is a rare moment of public rancor between the intelligence agencies and Ms. Feinstein’s committee, which has been criticized in some quarters for its muscular defense of many controversial intelligence programs — from the surveillance operations exposed by the former National Security Agency contractor Edward J. Snowden to the Obama administration’s targeted killing program using armed drones.

The origins of the current dispute date back more than a year, when the committee completed its work on a 6,000-page report about the Bush administration’s detention and interrogation program. People who have read the study said it is a withering indictment of the program and details many instances when C.I.A. officials misled Congress, the White House and the public about the value of the agency’s brutal interrogation methods, including waterboarding.

The report has yet to be declassified, but last June, John O. Brennan, the C.I.A. director, responded to the Senate report with a 122-page rebuttal challenging specific facts in the report as well as the investigation’s overarching conclusion — that the agency’s interrogation methods yielded little valuable intelligence.

Then, in December, Mr. Udall revealed that the Intelligence Committee had become aware of an internal C.I.A. study that he said was “consistent with the Intelligence Committee’s report” and “conflicts with the official C.I.A. response to the committee’s report.”

It appears that Mr. Udall’s revelation is what set off the current fight, with C.I.A. officials accusing the Intelligence Committee of learning about the internal review by gaining unauthorized access to agency databases.

In a letter to President Obama on Tuesday, Mr. Udall made a vague reference to the dispute over the C.I.A.’s internal report.

“As you are aware, the C.I.A. has recently taken unprecedented action against the committee in relation to the internal C.I.A. review, and I find these actions to be incredibly troubling for the committee’s oversight responsibilities and for our democracy,” he wrote.

The letter gave no details about the “unprecedented action,” but Mr. Udall said that it was important for the committee to “be able to do its oversight work — consistent with our constitutional principle of the separation of powers — without the C.I.A. posing impediments or obstacles as it is today.”

Mr. Obama ended the C.I.A.’s detention program in one of his first acts in the Oval Office, and he has denounced the interrogation methods as illegal torture.

Mr. Udall and Mr. Brennan had a testy exchange about the internal C.I.A. document in January, during one of the committee’s rare open hearings.

“Were you aware of this C.I.A. internal review when you provided the C.I.A.’s official response to this committee in June of last year?” Mr. Udall asked.

“It wasn’t a review, Senator, it was a summary,” Mr. Brennan responded. “And at the time, no, I had not gone through it.”

Mr. Brennan, who was a senior C.I.A. official at the beginning of the Bush administration when the interrogations were first begun, has found himself in an awkward position.

During his confirmation hearing last year to become C.I.A. director, he said that he had always been opposed to the techniques and that he had voiced his opposition to other agency officials. He did not say to whom he had expressed these misgivings, and former C.I.A. officials at the time said they could not recall Mr. Brennan’s having opposed the program.

In a statement last year, Mr. Brennan said that the interrogation methods once used by the C.I.A. “are not an appropriate method to obtain intelligence” and that “their use impairs our ability to play a leadership role in the world.” But he has sparred frequently behind closed doors with Senator Feinstein about the committee’s voluminous report.

The Senate’s investigation into the C.I.A. program took four years to complete and cost more than $40 million, in part because the C.I.A. insisted that committee staff members be allowed to review classified cables only at a secure facility in Northern Virginia. And only after a group of outside contractors had reviewed the documents first. Information about the Illuminati click here