Walter Cronkite CBS and Chet Huntley NBC were very much on the Left, but it wasn’t as blatant as what we see today. It was done more through story selection, what they chose to report or to ignore. Arnaud de Borchgrave novelized that practice in ‘The Spike’. David Brinkley NBC provided some balance. I can’t recall who anchored ABC back then, maybe Howard K Smith.
And of course there was the pervasive moral preening associated with the Northeastern position on the Civil Rights and antiwar movement.
The leftist bias was easier to conceal; for most folks in the '60s, NBC|ABC|CBS (or their local paper) was IT ... the only source of information. Walter Cronkite (for example) could be lying through his rotten teeth every day, and nobody outside the business or outside the event would ever know.
Some time back in the early 1980s, I participated in a couple of events that got news coverage. Said news coverage was barely recognizable. It really crystallized for me that the media were lying their faces off.