Bill Burkett, the man identified yesterday by CBS as the source of the controversial documents used in its September 8 “60 Minutes II” report questioning President Bush’s Air National Guard service, plans to sue the network, according to Mr. Burkett’s former lawyer, David Van Os.

For a dozen days, CBS aggressively defended the Dan Rather story against withering criticism from documents experts, conservatives and others who said it made use of phony documents. The report centered on purported memos by a now-deceased National Guard squadron commander, Lt. Col. Jerry Killian. The memos, for Killian’s files, said that Mr. Bush disobeyed an order to undergo a physical and that pressure was brought to bear to “sugar coat” Mr. Bush’s Guard service.

CBS reversed its position yesterday. CBS News’s president, Andrew Heyward, released a statement calling the use of the documents “a mistake which we deeply regret.”

“Based on what we now know, CBS News cannot prove that the documents are authentic, which is the only acceptable journalistic standard to justify using them in the report,” Mr. Heyward said. “We should not have used them.”

The CBS statement said: “Burkett … admits that he deliberately misled the CBS News producer working on the report, giving her a false account of the documents’ origins to protect a promise of confidentiality to the actual source.”

Mr. Rather attached a statement to the CBS News release, saying, “I find we have been misled on the key question of how our source for the documents came into possession of these papers.”

Mr. Van Os, the lawyer, said in a telephone interview with The New York Sun that his former client had “several meetings with lawyers to determine the best course of action.” He said the planned lawsuit would center on what he termed “defamation of character and libel.”

Mr. Van Os declined to name the attorneys Mr. Burkett consulted with, nor would he discuss why he is no longer representing Mr. Burkett. Mr. Van Os is currently running as a Democrat for the Texas Supreme Court.

Mr. Burkett “told me everything about the process” of his dealings with CBS and how he came into possession of the documents at the heart of the controversy, the lawyer said.

It was Mr. Burkett who was misled, according to Mr. Van Os. The lawyer said the CBS News producer, Mary Mapes, promised to protect Mr. Burkett with complete anonymity and CBS was to “expend both time and money authenticating” the memos.

“Bill Burkett went with CBS News on this over ABC News, the New York Times, and the Washington Post because they promised to work the hardest to protect him and authenticate the documents. ,” Mr. Van Os told the Sun. “Bill leveled with [CBS] about his doubts over the papers, and they promised him they would take their time. They spent all of three days, maybe less, on authentication.”

Ms. Mapes declined to comment, said a CBS spokeswoman, Kelli Edwards.

Mr. Van Os conceded, however, that his client “was not direct” about where he got the memos, “to protect a promise he made to the man who gave them to him.” He said Mr. Burkett’s lies “pale in comparison to CBS’s.”

Mr. Burkett, in an interview with Mr. Rather broadcast yesterday on the “CBS Evening News,” said he was pressured by CBS to reveal his source for the documents. “I simply threw out a name that was basically, I guess, to get a little pressure off for the moment,” Mr. Burkett said.

He said he didn’t forge any documents.

“I didn’t totally mislead you,” Mr. Burkett told the anchorman. “I did mislead you about one individual.” His former lawyer said Mr. Burkett was little more than a “passive receptacle” for passing on the documents. Mr. Van Os described Mr. Burkett as a struggling rancher – and frequent Bush administration critic – who received a phone call one night in late February, after an appearance on the MSNBC show “Hardball” in which he was critical of Bush administration policies.

The caller asked Mr. Burkett to go to Houston to view “some important paperwork” detailing Mr. Bush’s record of service in the National Guard.

Mr. Burkett told the caller, whom Mr. Van Os identified only as “a Texas man with Air National Guard experience,” that he would not go to Houston for that but would be in the city March 4 for the Simmental cattle show, said Mr. Van Os.

At the show, a man approached the booth manned by Mr. Burkett and gave him a manila envelope with the now-controversial documents in it.

Mr. Van Os said Mr. Burkett has repeatedly maintained to him that he did not contact reporters or any political activists about these memos.

“He kept this under lock and key,” the lawyer said.

Asked about Mr. Burkett’s e-mail offers to help the Kerry campaign evaluate Mr. Bush’s Air National Guard service – reported by the Washington Post last week- Mr. Van Os said the offer was only to “help construct a President Bush service timeline” and “had nothing to do with the memos he had.” He said the Kerry campaign did not respond to Mr. Burkett’s offer.

In late May, however, Mr. Burkett began getting calls inquiring about the memos from “national newspapers and TV,” said Mr. Van Os. The lawyer said Mr. Burkett told the reporters that he declined to comment or said he knew nothing about the documents.

One organization was more persistent than the rest, said Mr. Van Os.

“CBS News called the most and promised the most [to Mr. Burkett],” Mr. Van Os said. “They said they’d been working on this story for five years and had other corroborating evidence [to support the memos].” Mr. Van Os said his former client was repeatedly told that all they needed was the documents and promised that Mr. Burkett would have nothing to do with the story.

On September 2, Mr. Van Os said, Mr. Burkett gave producers from CBS copies of the documents he had received in Houston, keeping the originals. He said Mr. Burkett received assurances that CBS would immediately begin an extensive authentication process.

“My [former] client is a struggling rancher who is broke-what the hell does he know about document [authenticity]?” said Mr. Van Os.

The lawyer said Mr. Burkett told him he knew there might be problems when he found out that CBS producers went to a Kinko’s in Abilene and faxed the copies to several document experts for verification purposes.

“I don’t know anything about this, but aren’t these experts supposed to see the [damned] things?” Mr. Van Os said.

On the evening of September 8, six days after CBS took delivery of copies of the memos, it broadcast a heavily publicized story alleging that the young George W. Bush used political pull to get away with minimizing his military duty. Using the memos as key evidence in its report, CBS News put PDF copies of the documents on its Web site.

At 11:59 p.m. on the night of the broadcast, a poster on the conservatives’ Web site Free Republic, going by the name of Buckhead, said the memos had typographical issues and spacing problems and could not have been created by a typewriter available in 1972. He argued that the documents were probably forgeries.

Until yesterday, CBS executives – most notably Mr. Rather – stood by the story and dismissed many of those who questioned it as “partisan political critics.”

Mr. Van Os, in reply to both Mr. Rather’s and Mr. Heyward’s new statements, called CBS “an organization with a total lack of moral or journalistic integrity.”

Mr. Rather’s assistant, Kim Akhtar, did not return a message seeking comment from the anchorman.

Mr. Burkett did not return several phone messages seeking comment.