The verdict in favor of CBS and Dan Rather in the slander suit brought against them represents a victory for the press, but not one achieved without cost.

Media malpractice appears to be emerging as a legal concept alongside medical malpractice, and for similar reasons--an erosion of confidence in the practitioners and an awareness of their capacity for doing harm.

That is evident in the attitude of juries that increasingly render heavy libel and slander judgments not only against Penthouse and the National Enquirer, but now against big mainstream enterprises.

Indeed, bigness appears to be a root of the problem. The Big Media are replacing Big Government as a metaphor for unresponsive self-interest, self-perpetuating and self-justifying.

Television news practices are under challenge. Routine tinkering with reality--reverses, cutaways, retapings, sharpened-up questions and answers--look suddenly suspect when pried from reluctant hands for courtroom screening.

Its stars look less stellar when summoned from the anchor desk to the witness stand. But Dan Rather must have known that something was changing when he got into an argument a few years ago, with a Chicago taxi driver and found Chicagoans siding with the taxi driver.

One of the things that is changing is that the public no longer regards the press as its defender against the establishment, but as the establishment --as a big business less concerned with rights than with ratings.

The tradition of the crusading reporter with press card in his greasy hatband began fading with studio hair-styling and died with multimillion-dollar superstar contracts.

Unloved by the public, the news establishment is also unloved by other vested interests. When President Nixon had Vice President Spiro T. Agnew attack television journalism as "a tiny and closed fraternity of privileged men," he was only one of a succession of presidents who found the media an inviting target. Chief Justice Warren Burger, from the highest bench in the land, has denounced "the big media empires." And even an exile from the Soviet propaganda machine, Solzhenitsyn, has discovered America to be foundering in the grip of the "misleading media."

A voice of conscience from inside the industry, Charles Kuralt, has said the fault lies with media executives, who have lost "the ancient faith," now displaying "greater responsibility to the bottom line than to the public good."

Whatever it is that has changed, it is clear that Americans will no longer forgive us our press-passes. Perhaps we will have to earn anew the immunities we claim by showing that our purpose is more to trouble the strong than trample the weak.

What we must do, if you will pardon the expression, is clean up our act.