Bob Woodward apologized to The Washington Post yesterday for failing to reveal for more than two years that a senior Bush administration official had told him about CIA operative Valerie Plame, even as an investigation of who disclosed her identity mushroomed into a national scandal.

Woodward, an assistant managing editor and best-selling author, said he told Executive Editor Leonard Downie Jr. that he held back the information because he was worried about being subpoenaed by Patrick J. Fitzgerald, the special counsel leading the investigation.

"I apologized because I should have told him about this much sooner," Woodward, who testified in the CIA leak investigation Monday, said in an interview. "I explained in detail that I was trying to protect my sources. That's job number one in a case like this. . . .

"I hunkered down. I'm in the habit of keeping secrets. I didn't want anything out there that was going to get me subpoenaed."

Downie, who was informed by Woodward late last month, said his most famous employee had "made a mistake." Despite Woodward's concerns about his confidential sources, Downie said, "he still should have come forward, which he now admits. We should have had that conversation. . . . I'm concerned that people will get a mis-impression about Bob's value to the newspaper and our readers because of this one instance in which he should have told us sooner."

The belated revelation that Woodward has been sitting on information about the Plame controversy reignited questions about his unique relationship with The Post while he writes books with unparalleled access to high-level officials, and about why Woodward denigrated the Fitzgerald probe in television and radio interviews while not divulging his own involvement in the matter.

"It just looks really bad," said Eric Boehlert, a Rolling Stone contributing editor and author of a forthcoming book on the administration and the press. "It looks like what people have been saying about Bob Woodward for the past five years, that he's become a stenographer for the Bush White House."

Said New York University journalism professor Jay Rosen: "Bob Woodward has gone wholly into access journalism."

Robert Zelnick, chairman of Boston University's journalism department, said: "It was incumbent upon a journalist, even one of Woodward's stature, to inform his editors. . . . Bob is justifiably an icon of our profession -- he has earned that many times over -- but in this case his judgment was erroneous."

Shortly after Woodward's conversation with Downie in late October, a federal grand jury indicted Vice President Cheney's chief of staff, I. Lewis "Scooter" Libby, on charges of perjury and obstruction of justice in the Plame case. Woodward told Fitzgerald that he met with Libby on June 27, 2003, but that he does not recall discussing Plame or her husband, White House critic and former ambassador Joseph C. Wilson IV.

Yesterday, White House Chief of Staff Andrew H. Card Jr. said that he was a source whom Woodward testified he spoke with during that period. But Woodward said that neither Plame nor Wilson came up during that conversation.

Fitzgerald has spent nearly two years investigating whether administration officials illegally leaked Plame's name to the media to discredit Wilson.

Exactly what triggered Woodward's disclosure to Downie remains unclear. Woodward said yesterday that he was "quite aggressively reporting" a story related to the Plame case when he told Downie about his involvement as the term of Fitzgerald's grand jury was set to expire on Oct. 28.

The administration source who originally told Woodward about Plame approached the prosecutor recently to alert him to his 2003 conversation with Woodward. The source had not yet contacted Fitzgerald when Woodward notified Downie about their conversation, Woodward said.

"After Libby was indicted, [Woodward] noticed how his conversation with the source preceded the timing in the indictment," Downie said yesterday. "He's been working on reporting around that subject ever since the indictment."

Once Fitzgerald contacted Woodward on Nov. 3 with a request to testify, the newspaper's lawyers asked that nothing be published until after the deposition, Woodward said.

The disclosure has prompted critics to compare Woodward to Judith Miller, a New York Times reporter who left the newspaper last week amid questions about her lone-ranger style and why she had not told her editors sooner about her involvement in the Plame matter. An online posting at Reason magazine called Woodward "Mr. Run Amok," a play on Miller's nickname at the Times. Neither reporter wrote a story on the subject.

Rem Rieder, editor of American Journalism Review, called Woodward's disclosure "stunning" and said it "seems awfully reminiscent of what we criticized Judith Miller for."

Times Executive Editor Bill Keller accused Miller of misleading the paper by not disclosing earlier that she had discussed Plame with Libby. Managing Editor Jill Abramson has said she has no recollection of Miller suggesting that she pursue a story on the Plame matter, as Miller has maintained.

In Woodward's case, he says he passed along a tip about Plame to Post reporter Walter Pincus in June 2003, but Pincus says he has no recollection of such a conversation. Pincus has also testified in the probe but, like Woodward, has not obtained permission from one source to disclose that person's identity.

Woodward has criticized the Fitzgerald probe in media appearances. He said on MSNBC's "Hardball" in June that in the end "there is going to be nothing to it. And it is a shame. And the special prosecutor in that case, his behavior, in my view, has been disgraceful." In a National Public Radio interview in July, Woodward said that Fitzgerald made "a big mistake" in going after Miller and that "there is not the kind of compelling evidence that there was some crime involved here."

Rieder said it was "kind of disingenuous" for Woodward to have made such comments without disclosing his involvement.

Liberal blogger Josh Marshall wrote: "By becoming a partisan in the context of the leak case without revealing that he was at the center of it, really a party to it, he wasn't being honest with his audience."

Downie said Woodward had violated the newspaper's guidelines in some instances by expressing his "personal views."

During the Watergate scandal, Woodward protected the identity of "Deep Throat" -- the government source who helped reveal Nixon administration corruption -- and kept the secret until former FBI official W. Mark Felt went public this spring. In this case, Woodward is protecting a Bush administration official who may be part of an effort to strike back at a White House critic. Woodward said he has "pushed" his source, without success, for permission to discuss the matter publicly.

Woodward and Downie said they doubt that The Post could have found a way to publish the content of Woodward's conversation, which under the ground rules established with the source was off the record. Woodward said that the unnamed official told him about Plame "in an offhand, casual manner . . . almost gossip" and that "I didn't attach any great significance to it."

Woodward said he realized that his June 2003 conversation with the unnamed official had greater significance after Libby was described in an indictment as having been the first administration official to tell a reporter -- the Times' Miller -- about Plame. Downie said he has told Woodward that he must be more communicative about sensitive matters in the future.

Woodward said that it was "pretty frightening" to watch Fitzgerald threatening reporters with jail -- Miller served 85 days for initially refusing to testify -- and that he "had a lot of pent-up frustration." Woodward said that he "was trying to get the information out and couldn't" because of his agreement with his source.

Woodward has periodically faced criticism for holding back scoops for his Simon & Schuster-published books, which are invariably trumpeted by The Post, and several Post staff members complained yesterday in in-house critiques of the newspaper about his role.

Downie said he remains comfortable with the arrangement, under which Woodward spends most of his time researching his books, such as "Bush at War" and "Plan of Attack," while giving The Post the first excerpts and occasionally writing news stories. He said Woodward "has brought this newspaper many important stories he could not have gotten without these book projects."

Woodward, who had lengthy interviews with President Bush for his two most recent books, dismissed criticism that he has grown too close to White House officials. He said he prods them into providing a fuller picture of the administration's inner workings.

"The net to readers is a voluminous amount of quality, balanced information that explains the hardest target in Washington," Woodward said, referring to the Bush administration.