NEW YORK -- Literary agent Rick Broadhead worked out, took a shower, ate dinner and settled into a chair earlier this month to watch a new episode of his favorite show, "The West Wing."

Yet it wasn't on. Less than 24 hours earlier, NBC executives decided to replace it with a "Law & Order" rerun, reasoning "The West Wing" would be crushed in the ratings by a baseball playoff game.

"I was incredibly disappointed," said Broadhead, a Toronto, Canada, resident. "It was a huge letdown. As a viewer, you look forward to it. You sometimes plan your evenings around certain shows."

Better keep those plans fluid.

Television schedules often seem written in disappearing ink, so it's worth asking: Is the whole idea of stable lineups becoming obsolete in a hypercompetitive, multichannel world?

"I think the world is completely different from when I grew up knowing that 'Happy Days' and 'Laverne and Shirley' were on ABC on Tuesday nights," said Jeff Zucker, NBC Entertainment president.

"There are still several appointment shows on every network -- probably more on NBC than anywhere else -- but beyond that, this idea that you have to set your 22 hours and that's the way it is is as arcane as running the repeats of those shows in the summer," he said.

Already this season, NBC has blown up its struggling Friday night lineup, moved "Third Watch" from Monday to Friday and taken the touted comedy "Coupling" off the air.

Some of NBC's schedules, particularly for Fridays, are set week to week, leaving so much uncertainty that a Washington Post reporter trying to keep track wryly called it "cubist origami."

Zucker is an aggressive businessman, and he's adopted several strategies designed to wring as many ratings points out of a night as he can. He's "supersized" popular shows, experimented with different time slots and aired programs on different nights for extra exposure.

He's intent on keeping NBC dominant among the 18-to-49-year-old demographic -- so far he's succeeded -- but the job is becoming more difficult in a season where no network can claim any new hits.

Like Broadhead, one television historian questions whether the price paid for frequent changes is alienating viewers.

"I have a lot of trouble keeping track of shows, and I do this for a living," said Tim Brooks, a Lifetime executive and co-author of "The Complete Directory to Primetime Network and Cable TV Shows."

'Certain amount of panic'

Over the past few years, broadcasters have been able to charge more for commercials even though fewer people are watching. Ratings are down again this season -- particularly among young people -- creating the prospect that networks will have to give refunds to advertisers.

"There's a certain amount of panic at the networks that they have to do something to stop this or the whole house of cards is going to fall apart," Brooks said.

ABC generally has kept its lineup of shows intact, while Fox delays the debuts of many of its shows because of postseason baseball.

CBS believes that maintaining a stable schedule provides a comfort level to viewers, said David Poltrack, the network's chief researcher. (CBS isn't immune to changes; "The Brotherhood of Poland, N.H." was just canceled).

"We think we have gained over the last several years by virtue of the fact that we have the least amount of change in our schedule," he said.

That's particularly important at a time when viewers are overwhelmed by so many choices, he said.

Research shows that a high percentage of viewers return to their favorite shows week after week -- the concept of appointment viewing -- and that hasn't changed much over the years, Poltrack said. What's broken down is the idea that viewers will stick with one network for a night; the remote control has set them free.

To a certain extent, that argues in favor of NBC's more aggressive approach. Better to grab them if more viewers are beginning their evenings with a look at on-screen guides and making decisions at the spur of the moment.

This time of year -- right before the important November ratings "sweeps" -- is particularly tough for schedulers. They must weigh, with only a few weeks of evidence, whether new shows should be nurtured or pulled from the lineup for strategic reasons. If a show comes back after a hiatus, viewers might not.

Zucker said his schedule flipping this year is exaggerated, probably because of the last-minute decision to pull original series on big baseball nights.

He's aware people complained, but considers that "nonsensical" and "silly." Since more people will watch the episodes on a non-baseball night, he's serving a greater number of viewers, he said.

Even Broadhead, when pressed, had to agree. "If I were an NBC executive, I might have done the same thing," he said.

But he vehemently objects to the idea that a stable television schedule isn't important.

Contrary to his image as an executive with an itchy trigger finger, Zucker said he's kept shows such as "Good Morning, Miami" and "Third Watch" on the air longer than some people advised to build an audience.

"There are appointment shows and appointment nights that you don't screw with," he said. "But, let's be honest, if people aren't watching a show -- i.e., 'Boomtown' Friday nights at 10 -- then whose greater good am I serving by letting it sit there and not changing the schedule?"