CBS News fired four executives and senior producers yesterday, after an independent panel concluded that a "myopic zeal" to beat the competition on a story about President Bush's National Guard service led to serious flaws in reporting the piece.

In a scathing 224-page report, the panel appointed by CBS identified a host of missteps that led 60 Minutes Wednesday to air an erroneous report and then staunchly defend it for almost two weeks despite mounting evidence that it was flawed. The network relied on an untrustworthy source, failed to verify key documents and tossed aside evidence that didn't support the story, the panel found.

"The fact is that basic journalistic steps were not carried out in a manner consistent with accurate and fair reporting, leading to countless misstatements and omissions in the reporting by 60 Minutes Wednesday and CBS News," the panel said in its report, released yesterday.

The panel consisted of Richard L. Thornburgh, a former U.S. attorney general and Republican governor of Pennsylvania; and Louis D. Boccardi, former CEO and president of the Associated Press. The panel interviewed at least 66 people, including 32 at CBS News, as part of its three-month investigation.

CBS News placed the entire report on its Web site yesterday, along with a statement from CBS Chairman and CEO Leslie Moonves acknowledging that "the system broke down" and that there were "lapses every step of the way."

It was unusually severe self-criticism for a network, but it reflected a desire for transparency in an era when news organizations are under increased scrutiny by critics looking for bias and errors.

The report comes as television networks and newspapers have been fighting to maintain credibility after several high-profile scandals. During the past two years, top editors at The New York Times and USA Today have resigned after reporters at the newspapers were found to have fabricated stories.

The original 60 Minutes piece, which aired Sept. 8, was based on four documents that alleged that Bush had received preferential treatment while in the Texas Air National Guard. The authenticity of the documents was quickly challenged online because their typeface was rare in typewriters at the time.

But yesterday's report identified much larger problems in how the story was reported and vetted, significantly a frenetic effort to get it on the air quickly, that compromised basic fact-checking. CBS received the documents Sept. 2 and aired its report just six days later.

By Sept. 20, amid mounting pressure, CBS disavowed the story and then formed the independent panel to investigate. As part of changes announced yesterday, CBS News will create the position of senior vice president for standards and special practices, to ensure fairness and accuracy in reporting.

CBS News President Andrew Heyward will keep his job and was largely spared in the report because he urged deputies in e-mail messages to get the story right, including one Sept. 7 that said: "We're going to have to defend every syllable of this one."

CBS Evening News anchor Dan Rather, who was the correspondent for the segment, has already announced that he will step down from the anchor desk in March. The panel reported that Rather apparently did not participate in the vetting of the segment and did not see it before it aired.

The employees who were dismissed are Mary Mapes, the producer of the National Guard segment; Josh Howard, the executive producer of 60 Minutes Wednesday; Mary Murphy, the senior broadcast producer of 60 Minutes Wednesday; and Betsy West, the senior vice president for CBS newsmagazines.

After the segment aired Sept. 8 and was questioned by mainstream news media, Heyward directed West to investigate the sourcing for the segment. She did not do so, the panel said.

But the panel's report lays much of the blame on Mapes, an Emmy award-winning producer who had helped break the story of detainee abuse at Abu Ghraib prison in Iraq. Mapes had earned a great deal of respect during 15 years at CBS News - such that colleagues did not challenge her on the Bush story.

Media scholars said they were most surprised by the systemic breakdown in journalism standards described in the report.

"The one thing that I find shocking is the extent to which the entire system at CBS News failed," said Kelly McBride, ethics group leader at the Poynter Institute, a journalism think tank in St. Petersburg, Fla. "You have one person doing very bad work - the producer, working on assumption, discounting contrary information and not being honest with her peers and superiors about what she knows.

"But then you have the executive producer not challenging her, not doing his job to make sure the process works, and you have the vice president [Betsy West] not doing what the president tells her to do."

The panel's report describes how Mapes made a series of errors in pursuing the story. Among them: