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.”

Don’t expect that to work.

“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 with no inkling of when it will return.

Like Broadhead, one television historian questions whether frequent changes alienate 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.”

ABC generally has kept its lineup of shows intact, while Fox delays the debuts of many of its shows because of postseason baseball — a highly rated primetime product this year.

CBS believes that maintaining a stable schedule provides a comfort level to viewers, said David Poltrack, the network’s chief researcher.

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

“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?”