A year ago at this time, it was unanimous: ABC would be the winner again in the prime-time network TV season that lay ahead. But the final ratings for the year proved otherwise. CBS won the season to one-tenth of a rating point and is now the front-runner for the new season starting in September as well.

Most of the experts were wrong. What happened?

"ABC made the classic mistake of overconfidence," says Herb Jacobs, one of the experts. Jacobs is a veteran TV consultant and sometime show-doctor who shuttles between L.A. and Palm Springs and says. "The people at ABC thought they could do no wrong. But they could."

ABC overconfidently moved hit shows around to new time slots and ruinously tinkered with such smasheroos as "Mork and Mindy," dumping the family characters who had apparently made viewers comfortable and adding new characters as kookie as Mork, plus occasional sex jokes that were probably supposed to woo adults but ended up alienating the family trade. "Happy Days" and "Laverne and Shirley" saw their ratings dwindle, even after ABC made red-faced reversals of earlier schedule changes. Both shows will be lucky to last one more season.

"ABC got mugged -- BY ITSELF," writes Jacobs in his latest, just-issued foreeast of the TV season. CBS will retain its leadership -- if not regain its long-lost luster -- until at least the end of the calendar year, Jacobs predicts. He awards CBS first place on most Monday, Friday and Sunday nights: ABC will win Tuesdays, Thursdays and Saturdays, and poor old NBC only gets Wednesday.

That means Fred Silverman won't be able to keep his promise to make NBC No. 1 by Christmas? "No, I don't think he'll be first," says Jacob from Los Angeles. "He won't even be a good last." He doesn't think Silverman could have done it even with the Moscow Olympics and the promotional showcase they would have provided for new fall shows.

"I would say this: Fred probably would have gotten a little more sampling of his new shows with the Olympics," says Jacobs. "But when he had the Olympics on ABC, he also had solid shows on the air. The play's the thing. If you have nothing, you get nothing, no matter how hard you promote it."

Jacobs, too, has heard now common-place industry scuttlebutt that Silverman himself will be canceled by RCA management, perhaps as soon as November ("They always fire the top executives in November," says one NBC insider. "That way the new team coming in can say the fall schedule wasn't their fault.") Of course, rumors of imminent departures are always imminent in television, but Jacobs says the current crop grew not in Hollywood but on Wall Street -- "from pretty high, pretty knowledgeable" sources.

Next season's flops? Why, we've got tomorrow's flops today. Jacobs thinks that on ABC, the early departures will include "Those Amazing Animals," a four-legged "Real People," and "Breaking Away," a series adapted from the popular movie. On CBS, "Ladies' Man," "Feeble and the Bean" and "Enos" get one-way tickets to Palookaville.And on NBC, Jacobs predicts quick demises for "Speak Up, America," "Harper Valley PTA" and the holdover "Facts of Life."

The flops, as usual, will far outnumber the hits, and Jacobs does anything with words but mince them. Of the Danny Thomas comeback show on ABC. "I'm a Big Girl Now," with Danny in another of his bellowing papa roles, Jacobs notes in his forecast that both the character and the format are "moldy" and that, "When this one is interred, someone should put a stake through its heart to make certain it doesn't get another go-around."

Those who loved the movie "Breaking Away" won't be a sufficiently large group to guarantee success for the TV series version, according to Jacobs, who has seen the pilot and says, "It's a very slow-moving, confused thing. I enjoyed the movie. But if you have to see these kids floundering away every week, it's no fun. The director should be shot."

Jacobs picks the CBS cop show "Freebie and the Bean" (from a movie, but with a male-female instead of a male-male cop team) as the worst excuse for a new series, and as for ABC's Ted Knight sex comedy "Too Close for Comfort," Jacobs writes, "Frankly, it's a bore." CBS is attempting to spin "The Dukes of Hazzard" off into another yahoo romp, "Enos," but Jacobs writes: "Selecting this bit of anemia to lead off an evening is like buying failure insurance."

NBC got big ratings when it ran the theatrical film "Harper Valley PTA" and so commissioned a series with the same title. But Jacobs says its star, Barbara ("I Dream of Jeannie) Eden, is too old now to have the necessary audience appeal. "Believe me, it's going to be nothing," he stoutly predicts. "Having this woman who's practically a grandmother prance up and down in mini-skirts is ridiculous."

Herb, you're cruel! "No, I'm honest."

Jacobs confirms there'll be more sex in TV shows next season, as if the world were crying out for that, and says the other obvious trend is toward informational or pseudo-informational programming in prime time. In his forecast, very few shows are predicted to end up in the blockbuster range -- 40 percent audience shares and above -- although a couple of years ago, there were several such programs on the air.

"Well, they're getting harder to make," Jacobs says. TV viewing patterns are changing, and the audience next season is likely to be spread out fairly evenly rather than rallying around huge mass favorites. This could be an early outward sign of the expected fractionalization of the audience that increased competition for the networks -- from cable, pay TV, all those other geegaws -- is supposed to bring about.

"I love this job," the seasoned and feisty Jacobs insists. "I've been in the business all my life. My only concern now is that I find the average age out here in production and programming getting younger and younger and younger, and these people have less and less experience. You sit next to one of these guys at a meeting and you ask him what he's done and he says he's been here and there and you find out it adds up to 2 1/2 years and he's a vice president!

"You take [NBC Entertainment President] Brandon Tartikoff. Brandon's a nice young man, but four years ago he was promotion director at WLS in Chicago! In four years he could not have learned what Cecil B. De Mille died knowing, and yet he's responsible every year for spending more money than De Mille ever saw in his whole life.

"When this sort of thing happens," Jacobs says discouragingly, "programming must get worse."