CBS newsman Dan Rather took the stand in his own defense today, testifying "there wasn't any doubt in my mind . . . this clinic was a phony" when he did a report on it for "60 Minutes."

"The single most important thing we had was the phony report signed by the doctor," Rather said. The clinic "specialized in turning out phony doctors' reports and . . . we had one signed by the doctor."

Rather, now managing editor and anchor for the "CBS Evening News," is testifying in a slander suit brought against him, producer Stephen Glauber and the network by Dr. Carl Galloway, a Lynwood, Calif., physician. In a 1979 "60 Minutes" report titled, "It's No Accident," about insurance fraud, Rather held up a phony medical report obtained by CBS investigators and said, "It was signed by Dr. Carl A. Galloway, M.D." Galloway, claiming his name was forged, filed a $30-million slander suit.

Galloway's attorney, Bruce A. Friedman, repeatedly objected to Rather's continuous references to "the doctor's signature." Superior Court Judge Jack W. Swink did not strike the references from the court record, but admonished the jury to consider them as evidence to Rather's "state of mind, not the truth of the event."

Rather, in charcoal-gray pinstripes, took the stand for the first time shortly before court recessed for lunch. He swore to tell the truth, "So help me God," climbed into the witness box, and, with some prodding by attorneys, came up with answers a little more distinguished than those usually heard in the Los Angeles Superior Court.

Occupation: "Anchorman and managing editor for the 'CBS Evening News.' "

"Who did you succeed in that job?"

"Walter Cronkite."

Accustomed to playing to millions on television every week night, Rather played well today in court. There is just enough Texas left in his voice to give it warmth. He looks at attorneys as they direct a question to him, then the gaze shifts and he looks at the jury while he answers. He has a great smile, and the Rather smile may play as well in a courtroom as the Rather pullover sweater did on television.

Rather described how a "60 Minutes" segment is produced, and more specifically, how "It's No Accident" came into being. He said that on his second trip to Los Angeles to film the segment, he was picked up at the airport by producer Stephen Glauber, and "Mr. Glauber was smiling, which he doesn't do very often."

Glauber's smile, Rather said, was the result of research by investigator Rosa Bravo, who went to the clinic three times, pretending to be a patient. "We knew," Rather said, "it was phony. We knew Rosa Bravo had not been to that clinic 19 times as stated in a bill from the clinic . . . There was no question, after we had that report, that we would go into the clinic . . . with the cameras rolling."

Some of the best scenes from this trial have happened outside the courtroom. Carol Gallo, who said she was a reporter for Human Events magazine, held a mini-press conference in the courtroom hall, accusing Rather of forcing her seat to be changed (away from Rather) because yesterday she had "told the clerk he was passing notes, which is against courtroom procedure."

Where does she get her knowledge of courtroom procedure? "I watch Perry Mason," she said.

Yesterday, CBS producer Glauber, in an effort to catch up with Rather on a courthouse escalator, shoved aside a local TV cameraman. The cameraman retaliated by kicking Glauber's right thigh.

Earlier in the day, when court was in recess, a few reporters were moaning to one another that the session hadn't produced anything interesting.

One reporter spotted Rather standing at a not-too-distant remove, pointed at him and said, "Maybe he could help. He's been at this longer than we have."

"What's that?" asked Rather as he strolled closer.

"A lead," the reporter said. "We need a lead."

Rather grinned. "I think it's my job here to see that you don't get one." The grin widened to a full-fledged smile. "But see me later and I'll write your story for you."