A Lot Has Changed in a Year for CBS : Television: Ratings news for the network isn’t all bad, but the killer is that it’s dead last in the contest for viewers 18 to 49 years old.

The reign of CBS as the nation’s most popular TV network has suddenly taken a sharp turn for the worse, despite “Murphy Brown,” “Murder, She Wrote” and “60 Minutes.”

These aging series--and David Letterman’s show--are just about the only regular night-time programs with real clout on CBS, according to ratings released this week for the first month of the 1994-95 season.

Letterman--who used to carve up his old boss, NBC owner General Electric--is now using his stiletto on his new employer, CBS, through some choice Top 10 lists. For instance, his “New CBS Promotional Slogans” included: “Where’s the remote control?” and “The shows are funnier if you’re drunk.”

Then there was another Top 10 list, “Ways CBS Can Improve Its Prime-Time Ratings.” Some suggestions: “Make ‘Murder, She Wrote’ topless” and “Create a new show about a family that sits down to watch ABC show.”

ABC has won the ratings three of the first four weeks.

With a noticeable lack of sizzle in its programming, CBS--after three years atop the pack, and the only network ever to jump from last place to first--has been heading from the penthouse back toward the basement.

It’s still early in the season, of course; CBS actually finished first one week and theoretically could come through in the stretch again. But what’s missing thus far is more than ratings.

Whereas things are popping at the other networks--with NBC’s new medical drama “ER” and its sitcom “Frasier” creating word-of-mouth, and ABC’s “Home Improvement” and “NYPD Blue” leading a pack of high-profile hits--CBS is definitely not the talk of the town, except for revived rumors about how its dropping ratings and profits are making it more vulnerable for a takeover, and for a considerably lower price.

The cold statistics, as of the latest weekly ratings, show that CBS is actually just three-tenths of a point behind leader ABC and two-tenths behind surprising NBC. But the killer for CBS is that it is dead last--way behind ABC and trailing even Fox--in the competition for viewers 18 to 49 years of age, whom advertisers prize. CBS targets a slightly older market but would dearly like to make inroads with younger viewers.

How is CBS management reacting to Letterman’s barbs?

“They have the brains to keep quiet about it,” says Letterman’s co-executive producer, Robert Morton. “I think they take it very well--because they’re ahead (with Letterman’s show). God forbid they weren’t ahead. I don’t think they’d take it that well.”

Adds Peter Lassally, also co-executive producer for Letterman: “There’ve been no complaints. They feel badly for us. The prime-time lead-ins don’t give us the boost we need.”

CBS spokesman Tom Goodman, speaking for network management, says of Letterman’s needling: “That’s what makes Dave Dave . Everybody’s fair game. Sometimes it’s more fun when he’s making fun of other people, but it’s all part of it.”

Says CBS’ chief programmer, entertainment president Peter Tortorici: “If I’m unable to laugh at myself, I ought to find another line of work. None of us here are that thin-skinned.”

But, as Morton says, “the lead-ins we’ve been getting are frightening--from prime time and local news.”

Tortorici acknowledges CBS’ nose-dive in generating viewer excitement: “Our problem is that we aren’t putting on big signature shows--shows that people are talking about. We came into this season hoping that ‘Chicago Hope’ (a medical series) would do this for us, but I have no less confidence in it than I did in ‘Picket Fences.’ ”

“ER” clobbered “Chicago Hope” in head-on competition, and the CBS series was moved.

“The biggest place we have to push,” says Tortorici, “is the half-hour comedy area. We haven’t had a monster comedy since ‘Murphy Brown’ years ago.”

While he touts such CBS sitcoms as “The Nanny” and “Dave’s World,” he also acknowledges that “they haven’t shown the kind of clout that a ‘Home Improvement’ or a ‘Frasier’ has.”

But, says Tortorici, CBS is preparing to roll out this season a number of situation comedies that he hopes will make a difference for the network. Among the shows he cites are:

“Cybill,” starring Cybill Shepherd as a divorced woman in her 40s with two daughters; “Under the Hood,” with George Wendt (Norm on “Cheers”) as a garage owner who has a radio show about cars; “Double Rush,” about bicycle messengers in New York City; and “Women of the House,” starring Delta Burke as a woman who inherits her late husband’s congressional seat.

Also: “The Office,” a workplace comedy with Valerie Harper, and “Heavens to Betsy,” the tentative title of a series with Dolly Parton as a woman who returns to her hometown after not quite achieving the success she sought as a singer.

Unless CBS does a major turnaround, Letterman may find himself in the position that Johnny Carson did at NBC when it was in a severe slump--virtually carrying the network with his late-night show. CBS’ successful grab of Letterman from NBC not only looks good now, but lucky, because he’s suddenly TV’s hottest property on a network that needs all the help it can get.

“If we don’t take the necessary steps to rebuild our lineup, we will continue to slide,” Tortorici concedes. “I saw it happen before, and I’m not going to let it happen again.”

It will be tough. On Tuesdays, for instance, where CBS used to weigh in powerfully with weekly movies, the competition now includes “Home Improvement,” “Frasier,” “Grace Under Fire” and “NYPD Blue.” Says Tortorici: “The landscape has changed.” CBS’ head of TV movies and miniseries left the network this week.

“Murder, She Wrote,” meanwhile, is CBS’ only Top 10 entertainment series this season. That says it all.

* HE’S STILL HERE: Conan O’Brien’s settles in--for another quarter at least. F12