(FORTUNE Magazine) – Television programmers dream about going into the fall season with the most-talked-about new show. This year Fox has bragging rights with 24. The stylish hour-long drama, starring Kiefer Sutherland as a CIA agent who has to stop a planned assassination of a black presidential candidate, plays out a single day over its 24 episodes.

But instead of anticipating a breakout hit, Fox is preparing to get the show exposure outside of its regular time slot. Miss 24 on Tuesdays? You can catch the same episode on Fox's sister cable network, FX, or even a second time on Fox's own air in the same week.

Television is entering a new paradigm, in which "must-see TV" is being replaced by "Play it again, Sam." All of the network executives at last month's Television Critics Association summer press tour in Pasadena said they are looking for ways to run their shows outside of the traditional weekly airing. As a result, ABC's Once and Again pops up on Lifetime; the WB will likely air Charmed on TNT, while parts of NBC's Law & Order franchise rerun on USA.

The reason? Dramas, especially those with continuing story arcs, rerun very poorly; hit programs such as ER and Ally McBeal have slumped to ratings nadirs this summer. Yet networks need multiple airings of those shows to recoup what they're paying in license fees for the big-budget shows that distinguish them from cable channels. So they sell the rights to cable, where the ratings bar is much lower.

ABC already has an agreement with its affiliate stations that allows the network to rebroadcast a quarter of its prime-time entertainment programs elsewhere. And according to Walt Disney President Robert Iger, his company's recent deal to acquire the Fox Family Channel is about having a second outlet to "aggregate" more viewers and ad dollars for its ABC network shows. Jeff Zucker, NBC's entertainment president, also sees some validity in this plan: "We may have to go to an economic model where the second run of some of these programs is on cable and elsewhere."

On the surface, that seems self-destructive for the broadcast networks--re-airing shows on cable could further chip away at broadcasters' audience share. But as ABC's Fox Family Channel pact demonstrates, these days owning shelf space--no matter its location on the cable box--is key. As ABC Television Network President Alex Wallau put it, "I would rather compete with myself than let somebody else do it."

STEPHEN BATTAGLIO is television editor for Inside.com.