Dan Rather vigorously defended his "60 Minutes" story on President Bush's National Guard service yesterday, saying the 30-year-old memos he disclosed on the show this week "were and remain authentic," despite questions raised by some handwriting and document experts.

"Until someone shows me definitive proof that they are not, I don't see any reason to carry on a conversation with the professional rumor mill," the CBS anchor said. "My colleagues and I at '60 Minutes' made great efforts to authenticate these documents and to corroborate the story as best we could. . . . I think the public is smart enough to see from whom some of this criticism is coming and draw judgments about what the motivations are."

The memos, described as having been written by Bush's squadron commander, Lt. Col. Jerry B. Killian, indicate that Bush got special treatment as a pilot in the Texas Air National Guard and failed to carry out a superior's order to undergo a physical exam. Several experts consulted by news organizations say the memos contain typographical and formatting features that suggest they were written on a computer or word processor rather than on an early 1970s government typewriter.

Rather said that CBS's lead expert was Marcel Matley of San Francisco, a member of the National Association of Document Examiners who has taught, lectured and written about his field, testified in numerous trials, and consulted for government agencies. Matley said last night that a "60 Minutes" executive had asked him not to give interviews.

The Dallas Morning News cast fresh doubt on the documents by reporting last night that the officer named in one memo as exerting pressure to "sugarcoat" Bush's military record was discharged a year and a half before the memo was written. The paper cited a military record showing that Col. Walter "Buck" Staudt was honorably discharged on March 1, 1972, while the memo cited by CBS as showing that Staudt was interfering with evaluations of Bush was dated Aug. 18, 1973.

The White House is raising doubts for the first time about the documents' authenticity. "I think there's a big question mark, like major news organizations are suggesting," communications director Dan Bartlett said last night. "Obviously, we see the same things that other people are pointing out now. But at the time, I had every reason to believe that a major news organization had authentic documents."

Killian's widow and son have also questioned whether the documents are real.

CBS News President Andrew Heyward staunchly defended the piece. "I have full confidence in our reporting on this story and in every reporter on both sides of the camera," he said last night. "This is going to hold up. This was thoroughly vetted."

Conservatives hammered Rather and CBS yesterday on talk radio and Internet sites. "I predict . . . that it's only a matter of time before CBS admits it was deceived," wrote Weekly Standard Managing Editor Richard Starr.

In an interview, Rather stressed that CBS had talked to two people who worked with Killian in the Texas Guard -- his superior, retired Maj. Gen. Bobby Hodges, and his administrative assistant, Robert Strong -- and both described the memos as consistent with what they knew of Killian. Hodges, who told CBS he was "familiar" with the documents, is an avid Bush supporter, and "it took a lot for him to speak the truth," Rather said.

Before airing Wednesday's segment, he said, CBS "vetted" the confidential source who provided the memos and concluded that "he did have the ability to get access to these documents and he was being truthful." Beyond that, Rather said, CBS consulted with military experts about Killian's language and the documents' format and compared them to other Bush service records previously released by the White House. "We decided there was a preponderance of evidence that they are what they purport to be," he said.

Asked if he was troubled by the handwriting and document analysts who say some of the typography and spacing did not exist in the early 1970s, Rather said he could not rule out the possibility of a hoax but sees no need for an internal inquiry.

Some CBS employees, who asked not to be identified while questioning their bosses' actions, expressed concern that the network had issued only a terse statement Thursday, when the authenticity of the documents was first questioned and until yesterday had refused to name any of the experts it had consulted or provide an on-the-record spokesman. One staff member, who has examined the documents but did not work on the "60 Minutes" piece, saw potential problems with them: "There's a lot of sentiment that we should do an internal investigation."

"The first rule of public relations is to get all the bad news out right away," said Tobe Berkovitz, associate dean of Boston University's College of Communication. "It looks like CBS News has made some serious errors here, and if so, they should plead nolo contendere and not do the perp walk later."

Others at the network noted that the producer on the Texas Air National Guard segment was the highly regarded Mary Mapes, who helped "60 Minutes" break the Abu Ghraib prison scandal in Iraq.

"It's hard to separate legitimate concern from political blowback and propaganda," Heyward said.

On last night's "CBS Evening News," Rather defended the piece against what he called the "counterattack." He interviewed Matley, who said he concluded after comparing Killian's signature on the memos to other undisputed documents that "yes, it's the same person."

Rather noted the critics' claim that typewriters in the Vietnam War era could not produce a raised superscript, such as the letters "th," but he maintained: "Some models did." As for contentions that the memos were written in a more modern font called Times New Roman, Rather said: "The company that distributes this typeface says it has been available since 1931."

Other experts have told The Washington Post that the spacing between letters is suspicious for documents of that era. But Rather cautioned that the memos become less clear as they are downloaded and photocopied.

In the interview, Rather said the controversy should not detract from these questions raised by the program: "Did a wealthy oilman who was a friend of the Bush family come to the speaker of the Texas House and ask for preferential treatment for George Bush, and did he get it? Did or did not then-Lieutenant Bush refuse to obey a direct order from a military superior?"

In 1999, "60 Minutes" apologized, as part of a legal settlement with a Customs Service official, for reporting on a memo that was later found to be fake.

Matley, who told Rather last night that he knew the Bush documents would be professional "dynamite," has been involved in high-profile cases, including a 1997 controversy over purported John F. Kennedy documents. After "60 Minutes" cast doubt on those documents, the man who unearthed them, Lawrence Cusack III, retained Matley in a suit against CBS that was rejected in court. Matley could not vouch for the documents' authenticity.

Staff writer Mike Allen contributed to this report.