Mr. Blair is no longer welcome in the newsroom he so often seemed unable to leave. Many of his friends express anger at him for his betrayal, and at The Times for not heeding signs of his self-destructive nature. Others wonder what comes next for him; Thomas Kunkel, dean of the journalism program at the University of Maryland, gently suggested that the former student might return to earn that college degree.

But Mr. Blair harmed more than himself. Although the deceit of one Times reporter does not impugn the work of 375 others, experts and teachers of journalism say that The Times must repair the damage done to the public trust.

"To the best of my knowledge, there has never been anything like this at The New York Times," said Alex S. Jones, a former Times reporter and the co-author of "The Trust: The Private and Powerful Family Behind The New York Times" (Little Brown, 1999). He added: "There has never been a systematic effort to lie and cheat as a reporter at The New York Times comparable to what Jayson Blair seems to have done."

Mr. Jones suggested that the newspaper might conduct random checks of the veracity of news articles after publication. But Tom Rosenstiel, director of the Project for Excellence in Journalism, questioned how much a newspaper can guard against willful fraud by deceitful reporters.

"It's difficult to catch someone who is deliberately trying to deceive you," Mr. Rosenstiel said. "There are risks if you create a system that is so suspicious of reporters in a newsroom that it can interfere with the relationship of creativity that you need in a newsroom — of the trust between reporters and editors."

Still, in the midst of covering a succession of major news events, from serial killings and catastrophes to the outbreak of war, something clearly broke down in the Times newsroom. It appears to have been communication — the very purpose of the newspaper itself.

Some reporters and administrators did not tell editors about Mr. Blair's erratic behavior. Editors did not seek or heed the warnings of other editors about his reporting. Five years' worth of information about Mr. Blair was available in one building, yet no one put it together to determine whether he should be put under intense pressure and assigned to cover high-profile national events.