BOSTON — NO tough-talking cops who break suddenly into song. No soul-searching characters who speak against somber background music.Not even young professionals struggling to find their way in the new society. They're all casualties - from "Cop Rock" to "Twin Peaks" to "thirtysomething" - of a conservative backlash reflected in the upcoming fall TV schedule. Reeling from the current "hitless" season - the worst in a long time - and from a fifth straight year of declining viewership, ABC, CBS, and NBC have taken TV's traditional tack in times of trouble: retreating defensively into the known. The networks are leaning on tried-and-true formats and on solid names like Carol Burnett, Sam Waterston, Marsha Mason, and James Garner. And they are assiduously avoiding risks - like the bad vibes stirred up in some viewers by ABC's creatively venturesome (and now dropped) "China Beach," set during the Vietnam War. The past season was launched with great hopes and a number of conceptually daring new shows. But from the 32 programs offered, only 12 have survived. If this experience wasn't enough to scare networks away from new ideas, another factor was: The season has also witnessed the closest ratings' race in some 25 years. That's the kind of competitive squeeze that makes for drab viewing. "What it tends to produce is a tweedle-dum and tweedledee of offerings," notes Brian Stonehill, who teaches a media course on "how to become a sophisticated television viewer" at California's Pomona College in Claremont. "They're all looking over their shoulder at the other guy." This timid - even reactionary - philosophy can be seen in the distinctly nonexperimental tone of next fall's season - a lineup noticeably light on anything suggesting risk. There are more variety shows, more movie hours - and lots of comedy. ABC, in fact, is launching a Wednesday-night blitz: six sitcoms in a row. That format is traditionally a moneymaker - especially in reruns. "Hour-long programs are expensive, requiring multiple changes of scenery, car chases, etc." says Lynn Walters, associate professor of communications at Texas A & M. "Most half-hour sitcoms, on the other hand, are in one or two locations. Your primary expense is with the stars." One noted industry figure - Betsy Frank, senior vice president of the New York advertising agency Saatchi & Saatchi - says: "Comedies are among the highest-rated shows historically. And it's probably easier to get those ratings, to put it bluntly, than it is with dramas." Ms. Walters says that "Americans just want to be entertained. They're looking for humor. It's hard to sustain the drama in most hour-long programs - things like 'China Beach' or 'St. Elsewhere' and 'thirtysomething. Programs like those - sometimes called "episodic" TV because the same characters appear in new stories each week - require the kind of commitment that many observers think network viewers are quickly losing. "There's an overall decline in programs that require a sense of loyalty," says Ms. Frank. "There are now fewer total dramatic hours on the networks, because dramas tend to take too long to find an audience, if they're ever going to." In the current TV environment - with some 30 channels in the average home, and some homes having 50 or more It's almost impossible to launch a series that is going to require people to keep tuning in week after week," Frank says. "So the new schedule offers more shows that give the network a chance to attract a different viewer on Week Two than they did on Week One, and maybe bring back the person from Week One to Week Three." That kind of viewing represents a change, according to Mr. Stonehill. "It used to be that 'Monday' or 'Friday Night at the Movies' on network TV was an event," he says. "It was 'appointment TV.' People made a point of sitting down and watching a particular show. 'thirtysomething' had that role with a certain segment of the population. You didn't plan certain kinds of events on Tuesday nights because you knew those people were watching 'thirtysomething. Instead, at a time of stress, the networks turn hopefully to their proven strengths in specific formats. CBS will be adding - to the surprise of some - a third movie night. "CBS movies are better than anyone else's," notes Frank, "so why not add a third night if it gets you an audience? When a network schedules a movie where they didn't have one before, we who were estimating performance of programs can usually automatically add a couple of share points [a network's percentage of people who are watching TV]." NBC's schedule retains more drama than the other networks - especially of the kind that network is noted for, like "L.A. Law" and "Law and Order and it has added two new ones. Yet even NBC's drama quotient is down from last year. Fox has also undergone a kind of retrenching. Last year it tried to broaden its target audience by expanding to five nights a week. "This year," says Frank, "my sense is they're going back to their core audience of kids and young adults with offbeat shows like "In Living Color," a ribald topical satire. Fox - considered a network on its way up - hopes this move will help bolster its appeal in a medium growing less friendly to the "big three" networks year by year.