Scrambling to contain a crisis engulfing one of its most prominent on-air personalities, NBC will begin an internal investigation into Brian Williams, the embattled evening news anchor who has admitted he misled the public with a harrowing tale of a forced helicopter landing in Iraq.

The “fact-checking” inquiry, confirmed on Friday by several people in the network’s news division, will review not only the Iraq incident but also Mr. Williams’s reporting during Hurricane Katrina in 2005, as well as any other issues that arise during the investigation.

Richard Esposito, the head of NBC’s investigative unit, will lead the inquiry. Mr. Esposito does not report to Mr. Williams, who holds the positions of both anchor and managing editor for “NBC Nightly News.”

In a staff memo on Friday, Deborah Turness, the president of NBC News, said that the network had “a team dedicated to gathering the facts to help us make sense of all that has transpired.”

Photo

The internal investigation will also include Brian Williams’s reporting after Hurricane Katrina. Credit Dwaine Scott/Sundance Channel

.

“Brian apologized once again, and specifically expressed how sorry he is for the impact this has had on all of you and on this proud organization,” Ms. Turness said in the memo, which was obtained by The New York Times.

NBC News executives have not publicly addressed the issue, hunkering down on Friday as Mr. Williams’s troubles continued to draw a frenzy of criticism. Across the web, commentators have been aggressive in questioning not only Mr. Williams’s reporting but NBC’s handling of the problem. Some military veterans and commentators have called for his resignation.

Executives canceled external meetings and said that the issue was absorbing all of their focus, people in the news division said. Current and former NBC employees discussed the ultimate fate of the news anchor, shocked by his fall from grace and the turmoil it had created at the network.

Mr. Williams has not addressed the issue publicly since Wednesday, when he apologized on his newscast for embellishing an account of an incident in 2003; over the years he came to say that he was in a helicopter that was hit by enemy fire, an assertion he now says is not true. On his newscasts Thursday and Friday, he did not mention the controversy.

If Mr. Williams is forced to step down, it would be a huge blow to the news division, which is in a cutthroat ratings race with the rival networks. In this season to date, NBC has averaged 9.3 million total viewers for its nightly broadcast, compared with 8.7 million for ABC and 7.3 million for CBS, according to Nielsen.

In addition to tarnishing Mr. Williams’s once pristine reputation, the scandal has led to broader questions about the management and the credibility of NBC’s news operations.

“NBC’s credibility is damaged by this because their principal news figurehead, which is really what an anchorman is, had some clear credibility questions distinguishing the truth from the reality,” said Mark Feldstein, a professor of broadcast journalism at the University of Maryland, who previously worked at NBC News.

NBC News executives and Mr. Williams were not made available for an interview.

For NBC, Mr. Williams is more than just a nightly news anchor. He’s a bona fide celebrity on par with Jimmy Fallon, Matt Lauer and Bob Costas in representing the face of the broadcast network. Should Mr. Williams be forced to step down, it is not clear who a successor would be, industry executives said.

READ MORE  HERE  AT THE NEW YORK TIMES WEBSITE