More than a quarter-century after its debut, “The Cosby Show” is still spoken of reverently in the world of TV for how it revived a genre and transformed a network.

In one of the major revelations of this fall TV season, ABC potentially has its own “Cosby” in “Modern Family.”

The second-year series has moved beyond critical raves — and its comedy series Emmy — into the ratings stratosphere, rising more than 20% vs. last year and this month becoming the most-watched entertainment series in adults 18-49 for the first time, and closing in on CBS’ “Two and a Half Men” and “The Big Bang Theory” as TV’s biggest-drawing sitcom overall.

“I think we always knew … that if we got a family comedy right, that would reach the broadest audience that network had to offer,” says ABC comedy senior veep Samie Kim Falvey. “The best part of it for us is we’ve taken the legacy of ABC family comedy and been able to update it and make it sophisticated in a way we’re proud of.

“I think in the back of our minds, coming into this fall, we really believed this (level of success) might happen, but most people were afraid to put it out there,” she adds. “I think that the comedy business has taught us humility over the past few years.”

That humility is what has ABC focused on not squandering the opportunity to use “Modern,” created by Steven Levitan and Christopher Lloyd, as a launching pad for bigger and better things for the network.

“If it’s a ‘Cosby Show’ or an ‘All in the Family,’ it can make a very big difference,” producer and former ABC, CBS and NBC programming head Fred Silverman says. “It creates an adjacency to a time period where you can develop other comedies, if it’s the right kind of a show.

“ABC was always a comedy network. If you go back and look at the most successful periods in its history, whether the ’60s with shows like ‘Bewitched,’ the ’70s or ’80s with shows like ‘Three’s Company’ and ‘Happy Days’ or ‘Roseanne,’ they’ve always had hit comedies. I think this is good, because they at least have got a foot in the door, but now the trick is … to build on it.”

Though comedies such as “Cheers” and “Family Ties” slowly gained an audience for NBC in the early 1980s, “Cosby” lit a fire under the Peacock, ultimately becoming TV’s most popular show for five consecutive seasons and lifting the comedies that followed into the top 10. NBC consequently reigned as TV’s top-rated network for the final years of the ’80s.

Also noteworthy is how “Everybody Loves Raymond” paved the way for CBS’ audience heights in the past decade. “Raymond” anchored CBS’ still-powerful Monday night lineup for years and provided a launchpad for long-running hit “Two and a Half Men,” which in turn went on to lift “The Big Bang Theory.”

Except for 1999-2000, when ABC rode the short-term boostof “Who Wants to Be a Millionaire,” the network has not been No. 1 since 1994-95. Not coincidentally, that was also the last time ABC had America’s top entertainment show — laffer “Home Improvement.”

The signs that “Modern” could presage an ABC revival extend beyond the show itself. None of the more than 20 comedies ABC premiered from 2004-2008 remain on the air, and the network hasn’t had a new sitcom make it to a third season since “Hope and Faith” (2003-06). But now, it appears ABC will break that streak three times over with “Modern,” “The Middle” and “Cougar Town,” validating the network’s gambit on four new comedies in 2009 from 8 p.m. to 10 p.m. Wednesdays.

“I’m not gonna lie,” Falvey recalls. “I had heart palpitations when I finally saw (last year’s) schedule.”

But everything save Kelsey Grammer starrer “Hank” survived, a feat largely attributable to the initial appeal of “Modern Family,” which finished in the top 20 as a rookie with a 4.0 rating in 18-49 (9.6 million viewers overall).

In particular, “Modern” provided support as a lead-in for “Cougar Town,” which spent a good portion of its freshman year rejiggering its focus in order to better connect with viewers. “Cougar Town” still squanders more than a third of the “Modern” audience, but it has lately built to its highest level since January.

“The Middle,” now opening Wednesdays for ABC at 8 p.m. after being birthed at 8:30 p.m. following “Hank,” also got a boost from “Modern” last season, when ABC began airing reruns of its hit show at 8. “Middle” is up more than 10% year to year.

In short, by elevating the night’s overall audience, “Modern” bought time for “Middle” and “Cougar” to build followings.

“I think that creatively we’re really, really happy with all of them,” Falvey says. ” ‘The Middle’ for us is kind of the unsung hero at 8. … ‘Cougar Town,’ we feel, is a show that really found itself creatively, and we still believe in Courtney (Cox) and the rest of their cast.”

Falvey also cites the promise of this year’s freshman, “Better With You.” Though the weakest of the four ABC sitcoms ratings-wise, it is on par with what “Middle” drew in the 8:30 p.m. timeslot a year ago.

Also relevant, Falvey says, is “Better With You” showing that ABC might be able to mix in multicam shows with the single-cam style of its returning Wednesday laffers. Though the family-centric concept has perhaps helped, shows might need to have that in spirit only.

“The great thing about ‘Modern Family’ — what is the universal blood type, O-negative? It really is the universal blood donor — it is compatible with so many different kinds of shows,” Falvey says. “That really frees you up to try a lot of different things.”

That includes the two midseason comedies on ABC’s horizon: workplace comedy “Mr. Sunshine,” starring Matthew Perry and Allison Janney, as well as “Happy Endings,” featuring a sextet of friends. Though ABC hasn’t formalized how it will bow the shows, one expects “Modern” will be a part of the plan.

“Certainly, we haven’t had a ‘Modern Family’ to launch a show behind,” Falvey says. “We want to make sure we’re giving the right kind of launch to a show, and we have to see how the rest of the fall season shakes out. It’s still kind of early.”

“Modern” is also having an impact down the development road, Falvey adds, with ABC open to low-concept pitches that emphasize verisimilitude (a style that could dovetail nicely with new ABC entertainment topper Paul Lee’s roots in cabler ABC Family).

“What’s great about a show like ‘Modern Family’ is that people are inspired to write about what’s really personal to them again. That authenticity comes out in the work and character development.”

The impulse to expand its comedy offerings will be a powerful one for ABC. For one thing, laffers are increasingly becoming a sturdy bet for broadcast television. Relative to the numerous new fall dramas that were DOA or on life support as soon as they premiered — amid widespread talk that cable can’t be beat when it comes to drama — broadcast comedies have flourished. Only Fox’s “Running Wilde” seems in jeopardy of a pre-winter cancellation.

And although ABC won’t benefit from the off-net sales of “Modern,” which comes from Twentieth TV, the robust dollars it recently racked up only add to Disney’s incentive to go deeper into comedy. It would be quite tempting for ABC to expand its half-hour offerings if “Modern” can turn another sitcom into a stalwart.

“It’s a very important show,” Silverman says. “They’ve got to use it as a building block while it’s still got the audience.”

But the challenge still remains.

“For every drama, you need two comedies,” Falvey says. “There is the practical aspect of that. As long as they’re great comedies, we’ll put them on the air. … We’ve made no secret of the fact that we have aspirations of opening another (comedy) night somewhere. We have to do it very carefully.”

That said, Silverman has his own thought of what comedy ABC should develop. Working title: “Mitchell and Cam” — i.e., a “Modern Family” spinoff of two of its popular characters.

“It’s a big enough cast,” he says. “They probably could take the gay couple and move ’em into an adjacent time p
eriod and have crossovers and basically have an hour show. I’m sure they’ve thought of it.”