Bob Woodward said yesterday that he notified his editor at The Washington Post of his involvement in the CIA leak case because he realized he "was going to be dragged into this."

In an interview with CNN's Larry King, Woodward, a Post assistant managing editor and best-selling author, detailed the events that led him to apologize to Executive Editor Leonard Downie Jr. for not notifying him earlier that a senior Bush administration official had told him about CIA operative Valerie Plame in June 2003.

In late October, Woodward said, he "learned another piece of this puzzle," which prompted him to go into "incredibly aggressive reporting mode." He said he called the source and asked about their earlier conversation involving Plame, the wife of White House critic and former ambassador Joseph C. Wilson IV. According to Woodward, the source said: "I have to go to the prosecutor. I have to tell the truth."

At that point, Woodward told King, "I realized I was going to be dragged into this, that I was the catalyst. And then I asked the source, 'If you go to the prosecutor, am I released to testify?' And the source told me, 'Yes.' "

Woodward testified before Special Counsel Patrick J. Fitzgerald last week but said the source would not release him from his pledge of confidentiality on the question of publicly discussing their off-the-record conversation.

He added: "Remember, the investigation and the allegations that people have printed about this story is that there's some vast conspiracy to slime Joe Wilson and his wife, really attack him in an ugly way that is outside of the boundaries of political hardball. The evidence I had firsthand -- a small piece of the puzzle, I acknowledge -- is that that was not the case."

He said the source told him Plame was a CIA analyst on weapons of mass destruction. In his experience, Woodward said, such analysts are not undercover. Fitzgerald has said Plame had covert status.

Asked how he could have discussed the Fitzgerald probe, on King's show among others, without revealing his involvement, Woodward said: "I try to give as much information as I can, but it is inevitable -- if I'm doing my job trying to dig into what's going on in the Bush administration, what is the nature of this war, what is the CIA up to -- that there are going to be things I know that we can't talk about, or I'm not going to bring up, most certainly."

Downie has said Woodward made a "mistake" in not informing him about the Plame conversation and should not have been voicing his opinions about Fitzgerald. Woodward told King he had to "find ways of expressing myself that don't look like I'm making a judgment or voicing an opinion, but offering analysis or, hopefully, some new facts."

Woodward said he was not trying to denigrate Fitzgerald by calling him a "junkyard dog." Woodward said he had often used the term to describe Michael Isikoff, a Newsweek correspondent who once worked at The Post and who was on a CNN panel last month when Woodward offered the description.

In an MSNBC interview in June, Woodward said of Fitzgerald, "His behavior in my view has been disgraceful." He said yesterday that he meant "it is disgraceful that we have an investigation where reporters are being subpoenaed." He also said Fitzgerald was "quite respectful of the First Amendment" during last week's deposition.

Asked if the episode has hurt his reputation, Woodward said, "That's for other people to judge."

Bob Woodward spoke to CNN's Larry King.