I read with astonishment and disbelief the column by Edwin M. Yoder Jr. concerning the ''fairness doctrine'' {op-ed, Aug. 18}. Especially: ''Broadcasters long ago made the awful mistake of surrendering to advertisers ('sponsors' in the evasive language of this overcommercialized industry) the privilege of dictating program content and time slots.The practice devalues the 'journalistic' ingredient in broadcasting.''

This belief is one of the hoariest canards still spread by uninformed print journalists. I spent 20 years working for newspapers and magazines before turning to television journalism with CBS News in 1953. Please take my word, as a veteran of its rewrite bank and city desk, that the late great New York Herald Tribune paid far more attention to the editorial judgments of its lawyers and advertisers than CBS News ever has.

Advertisers never had anything to do with the content of CBS News programs. They could withdraw their sponsorship from a particular program if they didn't like the subject matter, but they had no say whatever in how it was reported and edited.

During the Vietnam ''war,'' CBS presented far tougher news coverage of it than The Post and began doing so long before The Post saw the light.

I produced for CBS dozens of one-hour special reports about Vietnam, beginning in 1964. Some of the networks' affiliated stations hated those shows, but neither they nor any advertiser ever influenced their content or presentation. Never. Beginning in 1967 I was the executive producer for nearly five years of "The CBS Evening News With Walter Cronkite," then the nation's largest source of world and national news. We edited the daily news as we saw it, not as any sponsor saw it.

-- Leslie Midgley