NEW YORK - Network executives spend much of their time this month in darkened rooms, watching pilots for new shows and guessing which can become hits.

Some of the guesswork is gone at CBS and NBC, where additional spinoffs of "CSI: Crime Scene Investigation" and "Law & Order" are already penciled in.

They're the franchises, proven winners whose success is irresistible; it's no coincidence that CBS and NBC are the two most popular networks. The challenge comes in making sure expansion is not dilution, or that playing it safe ultimately doesn't make them sorry.

"They're like Dairy Queens popping up all over the terrain," Todd Holland, executive producer of Fox's recently canceled drama "Wonderfalls," said with a touch of envy.

The fourth "Law & Order" entry will be known as "Law & Order: Trial By Jury," and will star Jerry Orbach, who's spent 12 years portraying Detective Lennie Briscoe on the mother ship.

"CSI: New York," the third in that series, has two well-known actors as centerpieces: Melina Kanakaredes of "Providence" and Gary Sinise.

It's easy to see why both are being made. They're the closest thing in television to a sure thing. Each of the three previous spinoffs has succeeded, in a business where the vast majority of new series fail. ABC, for example, hasn't had a hit new drama in years.

Facing a room of reporters last week, CBS Chairman Leslie Moonves was willing to put his own money behind "CSI: New York."

"What show out there are you going to want to bet on more than that show?" he said. "I'll bet anybody in this room any amount of money that 'CSI: New York' is the highest-rated new show next season."

Jerry Bruckheimer, executive producer of the "CSI" series, admitted he was concerned that a spinoff would hurt the original show when CBS first approached him about making "CSI: Miami."

"As it turned out, it just bolstered the ratings for 'CSI,'" Bruckheimer said. "More eyeballs keep coming to it. The ratings kept going up and the ratings keep going up for 'Miami.'"

"Law & Order: SVU," the first drama to get the original's brand, was originally just titled "Sex Crimes," said Dick Wolf, its creator and executive producer.

He readily agreed to change the title to include the "Law & Order" brand. "Nobody involved in this had just fallen off a turnip truck," he said.

Wolf believes the three "Law & Order" shows -- and the new one he's writing -- are distinctive enough to work without the brand. They're not spinoffs in the sense that "CSI: Miami" is much the same show in a different city, he said.

"The value of the franchise is in the first six weeks that it's on the air, when there are 35, 36 new shows to sample," Wolf said. "The initial thrust of these shows is helped because the consumer says, well, I liked the last one, I might as well sample this one."

As a result, television is flooded with procedural crime dramas.

How much is too much?

A station manager at an NBC affiliate in Florida angered the network last fall when he publicly said the network was "like a one-trick pony. People like 'Law & Order' -- let's run it every night of the week."

ABC learned the dangers of overexposure the hard way a few years ago when it flooded its schedule with "Who Wants to Be a Millionaire" and drowned when the show collapsed.