The CIA has begun an internal investigation into whether a process designed to screen books by former employees and protect national security secrets is being used in part to censor agency critics, U.S. officials said.

The investigation coincides with the publication of a flurry of books from CIA veterans, and it is largely aimed at determining whether some redactions have been politically motivated.

Among the publications expected to get particular scrutiny is a memoir by the former head of the CIA’s clandestine service, Jose A. Rodriguez Jr., who used his book, “Hard Measures: How Aggressive CIA Actions After 9/11 Saved American Lives,” to mount a vigorous defense of interrogation methods that were widely condemned but that he asserts provided critical intelligence about al-Qaeda.

The target of the probe is the agency’s Publications Review Board. The PRB evaluates hundreds of submissions each year and is supposed to focus exclusively on whether publication of material would threaten national security interests.

The CIA declined to comment on the internal investigation or to answer questions about the composition and practices of the PRB.

U.S. officials familiar with the inquiry, who spoke on condition of anonymity, said that it reflects growing concern in the intelligence community that the review process is biased toward agency loyalists, particularly those from the executive ranks.

Members of the Senate Intelligence Committee expressed such concerns in a recent letter to CIA Director David H. Petraeus, a document that has not been publicly released.

CIA critics said the disparities in the review process are particularly apparent in books that deal with controversial subjects, including the agency’s use of waterboarding and other harsh interrogation measures in the aftermath of the Sept. 11, 2001, attacks.

A book released last year by former FBI agent Ali Soufan — who questioned al-Qaeda prisoners held by the CIA and has said he became dismayed by the agency’s tactics — was so heavily redacted that he published “The Black Banners: The Inside Story of 9/11 and the War Against al-Qaeda” with black marks across many of its pages to show readers how much he was forced to withhold.

In an interview, Soufan said that his book had been cleared by the FBI, but that the CIA fought to impose changes that included the redaction of comments taken directly from transcripts of public hearings on Capitol Hill.

Soufan said he was surprised at how much Rodriguez was allowed to disclose.

“Absolutely there are things that he was able to talk about that were redacted from my book,” Soufan said. “I think it has more to do with trying to protect a narrative rather than protecting classified information.”

Rodriguez’s book includes detailed accounts of interrogations and other operations while taking veiled swipes at Soufan and others who question the use of harsh interrogation methods.

Bill Harlow, a former CIA public affairs official who co-authored the Rodriguez book, disputed the assertion that he and Rodriguez were given favorable treatment.

“I don’t believe we were shown any special favors, and I know that the PRB insisted on removing several large chunks of material from the book,” said Harlow.

Soufan’s case was unusual because he never worked for the CIA. The PRB’s authority is grounded in the secrecy agreements signed by agency employees that require them to submit any material prepared for public disclosure “either during my employment . . . or at anytime thereafter.”

“The sole purpose” of the PRB review “is to assist authors in avoiding inadvertent disclosure of classified information,” according to a 1998 article published by the board’s then-chairman, John Hollister Hedley, in one of the few publicly available descriptions of how the panel works.

Authors who dispute the board’s findings often have little recourse other than to file a lawsuit in federal court. Failure to abide by the panel’s decisions carries penalties that include the forfeiture of any money made on sales of the book.

Some fights between authors and the PRB have landed in court.

Former CIA officer John Kiri­akou was charged by the Justice Department in January with lying to the PRB and leaking classified information. Prosecutors alleged that e-mails between Kiriakou and his co-author show the agency veteran sought to trick the board by claiming he was fictionalizing portions of his book, a charge that Kiriakou has denied.

In another recent case, U.S. prosecutors have sought to seize the proceeds from the publication of “The Human Factor: Inside the CIA’s Dysfunctional Intelligence Culture,” a book written by a former agency officer who bypassed the PRB and published under the pseudonym Ishmael Jones.

Even agency loyalists say their experiences with the board have been mixed. Henry A. Crumpton, a former top counterterrorism official, said that he generally found the panel to be reasonable, but that two redactions from his book, “The Art of Intelligence,” still have him scratching his head.

One passage “was very critical of the agency and of the administration and it was about a particular program,” Crumpton said in an interview. “That was really the only single item that I thought was driven by potentially political embarrassment as opposed to sources and methods.”

U.S. officials said the internal probe is not being conducted by the CIA’s inspector general. Former CIA officials said the agency sometimes assembles internal review panels that are separate from the inspector general, but agency spokeswoman Jennifer Youngblood declined to say whether that was true in this case.