CBS issued a damning independent review Monday of mistakes related to last fall's 60 Minutes Wednesday report on President Bush's National Guard service and fired three news executives and a producer for their "myopic zeal" in rushing it on the air.

CBS' 60 Minutes II questioned Bush's Vietnam War-era commitment to service in the Texas Air National Guard.

The review said CBS compounded the damage with a circle-the-wagons mentality once the report came under fire. The independent investigators added, however, that they found no evidence of a political bias against Bush. (On the Web: Full CBS panel's report)

CBS News President Andrew Heyward and Dan Rather, who announced in November he was stepping down as the anchor of CBS Evening News, escaped without any disciplinary action. But Rather, who narrated the Sept. 8 story and subsequent follow-ups, was criticized by CBS chief executive Leslie Moonves for "errors of credulity and over-enthusiasm." (Related video: 4 ousted at CBS)

"The system broke down on this one, for sure," said Louis D. Boccardi, retired chief executive officer of The Associated Press, who conducted the investigation along with former Republican Attorney General Dick Thornburgh. They delivered their 224-page report to Moonves last week.

Fired were Mary Mapes, the story's producer; Josh Howard, executive producer of 60 Minutes Wednesday ; Howard's top deputy, Mary Murphy; and CBS News senior vice president Betsy West.

The 60 Minutes story had questioned Bush's Vietnam War-era commitment to service in the Texas Air National Guard. Mapes began reporting the story in 1999, but the report centered on documents obtained only weeks earlier, supposedly written by Bush's commander, the late Lt. Col. Jerry Killian. The memos said that then 1st Lt. Bush did not take a mandatory medical exam and that Killian reportedly felt pressured to sugarcoat an evaluation of him.

CBS is the third major news organization to sustain a black eye recently: Top editors at both The New York Times and USA TODAY left in the wake of plagiarism and fraud scandals involving correspondents Jayson Blair and Jack Kelley.

For television news organizations, the incident rivals CNN's retraction of a June 1998 report that the U.S. military used sarin nerve gas in Laos during the Vietnam War, which led to correspondent Peter Arnett's departure. Former NBC News President Michael Gartner resigned under pressure in 1992 after Dateline NBC rigged crashes of General Motors pickup trucks to show alleged fire dangers.

As a result of Monday's report, CBS News said it had appointed one of its executives, Linda Mason, to a newly created job of senior vice president of standards and special projects, charged with thoroughly reviewing investigative stories before they air.

Both Moonves and the panel said it hoped the report did not have a "chilling effect" on CBS' commitment to investigative journalism.

Source: Agencies (condensed)