Now, a Pitch for Shows With Potential and Staying Power : Television: Some series got to be hits only after networks gave them time to build followings.

Now that the fall’s new TV series have arrived, the really difficult decisions begin for the networks.

Blockbuster events such as the “Murphy Brown”-Dan Quayle duel are aberrations. They sell themselves to the viewing audience.

But networks don’t live by smash hits alone. The winner is usually the programmer who can patiently nurse along series with promise and build a lineup of non-spectacular but solid shows to which viewers loyally return each week.

These are the backbones of network schedules--the dependable, long-running weekly programs ranging from CBS’ “Rescue 911” to ABC’s “20/20” to NBC’s “Empty Nest.”

And as the din of TV’s fall-season hype dies down, the most important network thinking is deciding which new borderline series show potential--and which plain-wrap, non-glitzy shows may have staying power to help build a strong bench.

Nothing thrills ABC, CBS, NBC and Fox like a new series that bolts out of the starting gate--an instant hit that immediately spells relief from increased financial pressure at the networks. CBS apparently has two of these in the sitcoms “Hearts Afire” and “Love & War.”

But there are really no other breakout hits this fall. And that calls for creative management, because ratings wars are won in the trenches. Series such as ABC’s “Full House” and NBC’s “Wings” may seem like big hits now, but only because they have grown with the help of good time slots, network commitment and the chance to sharpen their skills.

It is TV legend, of course, how “Cheers” started abysmally in the ratings but was allowed to grow by NBC management, which had faith in the comedy. It is still just as important to nurse along new shows.

Well, then, which new series, borderline in the ratings, seem worth nurturing?

None is potentially more appealing as a long-run entry than ABC’s new “Going to Extremes,” a one-hour medical school drama with a Caribbean setting that adds to the viewing experience like a long, cool drink.

Produced by the creators of “Northern Exposure,” another show that had to be nurtured, “Going to Extremes” started strong but hasn’t developed the unique personality promised in the high-rated premiere.

Those behind the show, however, think that Tuesday’s episode may be pivotal in establishing the consistent, specific tone that has been missing lately during a ratings slip. Even before the season began, “Going to Extremes” was referred to by insiders as “Southern Exposure.” But it simply shows too much promise for ABC to give it anything less than a full shot.

There really isn’t anything else new on ABC that’s worth going to bat for, even though the sitcom “Hangin’ With Mr. Cooper”--about a junior high teacher with two female roommates--has shown ratings potential.

CBS clearly has committed itself to such new comedies as “Bob,” with Bob Newhart as a cartoonist, and “The Golden Palace,” a reworking of “The Golden Girls” set in a Miami hotel. And both shows have paid off thus far.

What “Going to Extremes,” “Bob” and “The Golden Palace” have in common is that none of them will probably ever be a major hit, but all could become part of that firm foundation that really holds network TV together--the middling ratings success that can be depended on for amiable entertainment.

NBC has a few possibilities in this category that also have started out as middling ratings entries--”Mad About You,” about a newlywed couple, and “Rhythm & Blues,” about a black radio station that hires a free-wheeling, white disc jockey.

“Mad About You” is the classier of the two shows, especially in the chemistry between stars Paul Reiser and Helen Hunt. For that reason alone, NBC should go to bat for it in a major way.

Fox’s best new bet commercially may be “Martin,” another sitcom involving a black radio station. But the littlest network already has shown savvy in recent months by its buildup of the new “Melrose Place” on the heels of “Beverly Hills, 90210.”

You have to hand it to Fox for going where the other networks really are afraid to go--to prime-time comedy sketch series, which ABC, CBS and NBC consider suicidal in ratings competition. This is a great TV tradition that goes back to Ernie Kovacs, Steve Allen and the Sid Caesar-Imogene Coca “Your Show of Shows”--and Fox showed its best side when it presented Tracey Ullman’s sketch-style series and then gave us “In Living Color.”

This season, Fox has several more such sketch series, and the best is very good indeed, “The Ben Stiller Show.” It is, alas, scheduled against “60 Minutes,” and the ratings are predictably low--but the show is special stuff and is worth Fox’s special attention.

In truth, the Stiller show probably doesn’t have wide appeal, but, as with Ullman, Fox’s first Emmy winner, it could mean a lot to Fox’s image as a daring network. And don’t let our ifs and buts put you off: This is a very funny show with a very funny star.

ABC’s “Coach” is an example of a big success that really isn’t an innate powerhouse. Yet it grew into that category through intelligent network handling. And when “Coach” star Craig T. Nelson won the Emmy for best comedy series actor in August, the show suddenly had the prestige that escaped it all along.

The payoff for the growth of “Coach” is that it reportedly now gets $280,000 for a 30-second commercial, trailing only “Murphy Brown” ($310,000), “Cheers” ($300,000) and “Roseanne” ($290,000).

Building a winning network schedule is like piecing together a gigantic puzzle. In both, patience is the key.