Implicit through both hours and in the title of the CBS News special "When Television Was Young" is the idea that TV was primitive and silly in the '50s and has since grown to maturity.

One is tempted to say nothing could be further from the truth, except that we haven't seen the first Frost-Nixon show yet.

"When Television Was Young," at 9 tonight on Channel 9, is a fascinating and deplorable documentary filled with wonderful moments. It is poorly organized, flabbily written and blabbily narrated, but it brings back in blurry black and white intoxicating images from a time that looked on television more as wonder than menace.

The raw materials-kinescopes of early TV shows-are what makes the program. Its viewpoint is highly confused, but the area of '50s TV is a rich one. NBC had planned its own special, "TV: The Fabulous Fifties," to air Saturday night, but postponed it at the last minute because of its proximity to the CBS show. A new air date will be announced later.

Meanwhile, the '50s seem both only yesterday and 1 million B.C. The late but taped Ernie Kovacs rolls along in reruns on public TV, NBC has a "Fater Knows Best" reunion special set for May 15, and the top-rated network shows each week always include "Happy Days" and Laverne and Shirley," to sitcoms as mindless and irrelevant as anything that tickled a laugh track in TV's first decade.

CBS News not being the most funloving club in town, the "Television Was Young" special goes very heavy on the pop analysis and very light on the exposure of old footage. Narrator Charles Kuralt, who is a kind of walking pot-bellied stove, says, "We're not going to show you much of these old shows. Why betray memory? Your imagination is brighter than these old kinescopes."

Sorry Charlie, but those old kinescopes are a lot brighter than your commentary and producer Perry wolf's spell-it-all-out script. This really is one of the most fatuously overwritten documentaries ever; it insists that TV entertainment in the '50s was obsessively trivial, but it's got to occur to viewers that anything would be better than the pomposity and cant of a documentary like this one.

"The comedy of the '50s was about nothing," says Kuralt smugly, but little later we get to see a two-minute Sid Ceasar Pagliacci bit that is so brilliant it makes you want to cheer. Noel Coward and mary Martin knew they would "fail" on live TV, Kuralt says, yet in the next instant we see Coward doing "Mad Dogs and Englishmen" right smack into the camera, making his elegance and hauteur something you could almost reach out and touch.

What killed the real excitement of television was not just the takeover by tape and film but the development of TV's own professionals, including professional personalities like Kuralt, who have no talent but that of being able to come across on TV. In the '50s, the artists who ventured into TV from other fields shared their amazement and bemusement at the new medium with people equally amazed and bemused in their homes.

The program is on safer footing with its historyof TV news, and excerpts from early newscasts, with Douglas Edwards holding up still photos to the camera, are terribly amusing. A delve into the quiz show scandals unfortunately includes self-serving film of former CBS president Frank Stanton claiming cleanliness and promising reform. "Who did the cheating has never been made very clear," says Kuralt. It is very clear, however, that TV networks are responsible for what they put on the air.

Interrupting Kuralt's woeful solo are cherished and infamous faces and voices that tell the story of the '50s better than this CBS high school essay every could.

George Burns to Graice Allen: "How's your sister, Bessie?"

Ollie to Kukla: "I think we have a whole new art form coming up."

Joseph Welch of Joseph McCarthy: "have you no sense of decency, sir?"

Word printed on the flashing nose of a clown: "Hello"

Richard M. Nixon to the nation: "Our little girl, Tricia, the 6-year-old, named it Checkers."

Uncle Miltie steals an earring from morning for the very first time. Gleasa diva, Captain Kangaroo says goodson hoofs with Carney, Lucy brawls in a grape vat. Don Larsen pitches a perfect game and Edward R. Murrow presides at the first network linkup to show both the Atlantic Ocean and the Pacific Ocean, live, to a viewing nation.

"It was nothing," says Kuralt, precisely wrong in a way he could probably never understand. It was thrilling then and, somehow, it is thrilling now to see it again.

From a TV control room, Murrow assesses the electronic spectacle he has just witnessed. "We are impressed with the importance of this medium," he says. "We shall hope to learn to use it and not abuse it."

In the '50s, there were lots of songs about dreams coming true. Most of our dreams for television did not.