CNN won praises from media experts for dumping two veteran producers, reprimanding a star correspondent and publicly apologizing as it retracted a story about U.S. military use of nerve gas during the Vietnam War.

But some wondered whether it is enough to rescue media credibility, which has been battered by embarrassing incidents since May."We in the industry know that the worst things people say about us aren't true," said Sanford J. Ungar, a former newsman and dean of American University's School of Communication. "But it's getting harder and harder to defend ourselves."

At CNN's studio tour in Atlanta, Joe Mannon of Mena, Ark., was more direct. "You all do a poor job of sourcing," he said Thursday. "There used to be a standard. Now there's plagiarism. Pulitzers are returned."

Mannon spoke after CNN apologized to viewers and Vietnam veterans for "serious faults" in its June 7 "NewsStand" report on Operation Tailwind. The network alleged that the 1970 operation included the use of the deadly nerve gas sarin by U.S. commandos in killing American defectors.

The two main producers of the report, Jack Smith and April Oliver, were fired following a CNN-requested investigation by prominent media attorney Floyd Abrams. Senior producer Pam Hill resigned, while the lead reporter, Peter Arnett, was reprimanded.

Smith and Oliver said they stood by the "Valley of Death" story. "We presented the facts that we gathered," Smith said. "This was a report on America's secret army. There is no documentation."

Smith, who was a senior producer for "NewsStand," the joint CNN-Time newsmagazine, added that CNN's decision "will not send a chill through investigative reporting of secret military operations - it will freeze it."

Arnett received only a reprimand because he was not involved in much of the reporting, a CNN official said.

Tom Johnson, chairman of the CNN News Group, said network personnel bore full responsibility for its report and for the printed version that appeared June 15 in Time.

"CNN's system of journalistic checks and balances, which has served CNN exceptionally well in the past, failed in this case," Johnson said in a statement read on the air several times.

Time and the Pentagon said they had not found any support for charges in the report. CNN hired Abrams last week to investigate the accuracy of the report, and made its statement based on his probe.

Abrams concluded that CNN's reporting could not support the allegation that sarin gas was used, that American defectors were targeted or that they were even in the Laotian camp where the mission was carried out.

"The story wasn't there," Abrams said. "It was a bad mistake, and CNN has apologized for it, as I think they should."

While Abrams' report criticized the newsgathering, he said there was no suggestion that information was fabricated. If anything, he said, the serious flaws stemmed from the journalists' deep belief in the story and the way they discounted contrary information.

"That doesn't necessarily mean that the story isn't true," Abrams said on CNN. "But what it does mean then is that at this moment we simply do not have enough evidence, in my view, for any conclusion to be reached."

Pentagon spokesman Kenneth Bacon said its review would continue and likely would be completed within two weeks.