As broadcasters cool their heels during the summertime lull, a drama drought threatens to shake up the prime-time landscape. Luckily, a few new series look promising, although the shows that could have the biggest impact won’t premiere until mid-season.

With three months to go before the 2011-12 TV season gets under way, the Big Four are staring down a vortex. Many of the top dramas are now peppered with age spots—NBC’s Law & Order: SVU is on the verge of its 13th season; CBS stalwart NCIS is preparing its ninth campaign; and ABC’s Desperate Housewives and Grey’s Anatomy are both entering their eighth cycles—and there’s been a concomitant decline in ratings.

Last season, Desperate Housewives averaged 11.9 million live-plus-seven-day viewers and a 3.9 rating among adults 18-49, down significantly from its first-year heyday (23.7 million/10.7 rating). Fox’s seventh season of House served up its lowest deliveries, averaging 10.3 million viewers per episode, while Law & Order: SVU had its second-worst ratings performance. Only NCIS has bucked the trend; the naval procedural continues to grow in popularity, drawing its biggest numbers last season with an average draw of 19.5 million viewers.

Casting is also a major concern. House’s Lisa Edelstein, who portrayed Hugh Laurie’s boss and eventual love interest, checked out of the Princeton‑Plainsboro Teaching Hospital for good in May after she refused to accept a salary cut. SVU star Christopher Meloni recently announced that he won’t be back for a 13th season, and partner Mariska Hargitay will return for a truncated 13-episode arc.

Meanwhile, a number of top draws at other shows are in the final year of their contracts, including Laurie and Grey’s stars Patrick Dempsey and Ellen Pompeo. All three actors have suggested that they aren’t interested in renewing their respective deals.

Given that it boasts the five most-watched dramas on TV in NCIS, NCIS: Los Angeles, The Mentalist, Criminal Minds and CSI, CBS has little cause for concern. The network also has a proven favorite in The Good Wife, which averaged 13 million viewers in its sophomore run, and is home to the closest things to a new hit in Hawaii Five-0 and Blue Bloods.

With few holes in its lineup—CBS canceled a handful of series, including the long-running ghost story Medium and freshman buddy dramedy The Defenders—the Tiffany Network will premiere just three new dramas in the fall: Unforgettable, Person of Interest and A Gifted Man. A mid-season effort, the Robert De Niro-produced The 2-2, is also in the works.

Rival broadcasters have drawn buzz with their upcoming efforts. ABC’s Charlie’s Angels reboot has stirred up predictable interest from media buyers, as has its stylish ‘60s drama Pan Am. NBC is betting on its own period piece in The Playboy Club, as well as a remake of the U.K. detective series Prime Suspect, starring Maria Bello.

Fox’s big splash is likely to be the Simon Cowell effort The X-Factor, although the Monday night dino drama Terra Nova could draw sci-fi enthusiasts.

If the success of ABC’s Modern Family has helped engender a comedy boomlet—11 new sitcoms are set to premiere this fall, including sure things like CBS’ 2 Broke Girls and Fox’s New Girl—the most promising drama series won’t roll out until January at the earliest. Among the handful of mid-season gems are: NBC’s musical strip Smash, which was the most warmly received new offering unveiled during upfront week; the trippy JJ Abrams thriller Alcatraz (Fox); and ABC’s sudsy Good Christian Belles and the supernatural fright fest The River.

Buyers say they are cautiously optimistic that a few of the new dramas will resonate with viewers, but any hits will have to be established immediately. “The networks are so quick to pull the underperformers that a lot of shows just never have a chance at building a following,” said one national TV buyer. “But something’s got to give. The older shows are on their last legs.”

Another executive noted that the agita about a dearth of drama was reminiscent of a few years ago, when everyone with a keyboard and an Internet connection proclaimed that the comedy was dead and buried.

“CBS has established two comedy nights, and ABC and NBC are desperate to replicate that success this season,” said one cable exec. “So comedy’s back in a big way, so much so that you could argue that it’s become a defining genre. Hindsight being what it is, I have to imagine we’ll see a rebound in drama as well . . . and then we can all go back to saying comedy’s dead.”