Television executives' nightmare scenarios for 2008 are coming closer to reality as the Hollywood writers strike enters its sixth week Monday.

Renewed contract talks between the Writers Guild of America (WGA) and the Alliance of Motion Picture & Television Producers (AMPTP) broke off abruptly Friday, and industry executives see no end in sight to the worst Hollywood labor dispute in almost two decades.

The full effect of the strike will start to play across primetime in January. CBS, NBC and Fox have already outlined their first-quarter plans: midseason scripted shows, reality shows and judicious repeats. (ABC is expected to announce its strike-afflicted schedule early this week).

If the strike lasts another four to six weeks, it could spell the end for 2008 pilot production. The most-circulated scenario in that case involves the networks renewing all their existing series for next fall, producing their pilots in the summer and launching their new crop of shows in midseason 2009.

Such a disruption could imperil the annual upfront market in May, when the networks sell the bulk of their advertising slots for the next season. Uneasy ad buyers already are concerned about the expected audience erosion in the first and especially the second quarter.

There's been a lag in primetime with the strike. No one has felt the impact of it for the first weeks, said Brad Adgate, senior vp research at New York-based ad buyer Horizon Media. But (the networks) aren't putting their best foot forward (anymore). And the longer this thing is dragged out, the worse it's going to be in terms of scheduling.

One network executive said that it's tough to plan for something when you don't know how long you're going to be planning for.

We have all kinds of programming we can reach for, the executive said. I think the toughest part of planning for this is just the unknown. We don't know. Is this going to end in a week? Two weeks? A month? Two months? That's the toughest part.

The networks are starting to look at what to do about March and April and even later than that, depending on how long the strike lasts.

I'm really concerned about everybody but Fox starting in February, said Shari Anne Brill, senior vp at New York-based ad buyer Carat. Brill said Fox will be in good shape with American Idol and repeats of House, along with new programming like Terminator: The Sarah Connor Chronicles. That will offset the disappointment over 24. (Because of the heavily serialized nature of 24, Fox opted to hold the series instead of airing a partial season.)

Advertisers, who often worry that the programs they buy during the upfront negotiations might not be there later in the season, are now assured of it as the last original episodes of the fall series are played out and they all slip into repeats or are replaced. Some advertisers have pulled dollars because they likely won't be able to get the impact they expected. But there isn't a mass exodus, because first-quarter options -- the time when they could pull upfront commitments without penalty -- expired long ago.

But if the strike doesn't get settled soon, agencies and advertisers could exercise second-quarter options that are coming due in January. And if the networks underdeliver on their ratings guarantees -- and it's reasonable to assume that they will, given how nothing but American Idol will equal or better the delivery of originals of House, Grey's Anatomy or CSI -- the networks would have to give make-goods (i.e. free advertising slots) or even cash back.

ABC's serialized scripted hits don't repeat well, but the network has a deep bench of replacements as well as reality hits Dancing With the Stars and Extreme Makeover: Home Edition. On the other hand, CBS doesn't have that much inventory, but its crime dramas tend to repeat well, something that would be an advantage -- but only in the short term.

There's only so many times you can run the sprockets off something, Carat's Brill said. How many encores can you run?

CBS will hope to bring some magic to the broadcast network with the decidedly un-family-friendly serial-killer thriller Dexter and perhaps other series from sister cable network Showtime.

It probably speaks to how much they need scripted product, Brill said. They probably have the least backup of any network. There are seven episodes of 'Jericho.' Maybe they are wishing they had gotten more.

Fourth-ranked NBC has had a shaky start to the season even without a strike. But scheduling chief Vince Manze said Friday that it will have more original hours of programming -- scripted and reality -- in the first quarter than it did in first-quarter 2007. The growth comes mostly from unscripted fare -- as many as 11 hours a week -- as the network plans to air 85 hours of original scripted episodes, down from about 100 last year.

That includes returning Medium and Law & Order as well as Lipstick Jungle and recycled episodes of Law & Order: Criminal Intent, which had been relegated to USA. Friday Night Lights and Vegas were on an accelerated schedule, so there still are plenty of episodes.