A COUPLE of writers on “Law & Order: Special Victims Unit” huddled with a casting director. “What we need is the girl who looks like the adorable big sister, but then she turns out to be a pedophile’s accomplice,” an executive producer, Warren Leight, told his team.


Since its 1999 debut, “SVU,” the stalwart sex-crimes sibling of the original “Law & Order,” has delivered viewers a predictable, and beloved, formula of whodunit storytelling. Now the creator of the “Law & Order” brand, Dick Wolf — whose name is so tethered to television drama that just hearing it evokes an ominous chung-chung sound in many viewers’ minds — is branching out. He is taking his signature fast-paced realism (or what he calls “trompe l’oeil cinéma vérité”) outside New York to a Chicago firehouse. And unlike his strict procedural style, which gives little character back story, “Chicago Fire“ hinges as much on the messy personal lives of firefighters and paramedics as the fires, car accidents and other calamities they handle.


Mr. Wolf’s team calls “Chicago Fire,” which begins Wednesday on NBC, “Dick Wolf 2.0,” a slightly evolved approach for a big-name producer firmly committed to the creative doctrine that made “Law & Order” a billion-dollar property and one of the most lucrative franchises ever on television.


But “Law & Order” and its offshoots have taken a hit lately, a product of changing tastes in broadcast television toward character-focused dramas with story lines that stretch from episode to episode. For Mr. Wolf, after decades of prime-time ubiquity, the current television season represents a crossroads. The question is whether he can depart successfully from his formula, especially after his previous prime-time efforts to break with the format, the NBC show “Conviction” and ABC’s “L.A. Dragnet,” didn’t catch on. Early reviews of “Chicago Fire” have been mixed. (The Huffington Post said, “For a show about fire, it lacks any kind of spark.”) That raises the stakes for Mr. Wolf as he pushes into fresh territory unrelated to “the police who investigate crime and the district attorneys who prosecute offenders.”


In 2010 NBC canceled “Law & Order” after 20 years and more than 450 episodes. It canceled “Law & Order: L.A.” after a single season last year, which is when “Law & Order: Criminal Intent” concluded its run on USA. “SVU,” now in its 14th season, may outrank most other NBC dramas in the ratings, but the numbers have fallen since one of its stars, Christopher Meloni, departed in 2011.


“I have a very selfish agenda: my shows,” Mr. Wolf said over breakfast at the Four Seasons in New York. Newly slim, he adheres to the “cave-man diet,” eating only foods presumed to have been consumed in the Paleolithic era. He carries the luxurious leather briefcase of a high-priced defense attorney and wears orange socks with New Balance sneakers.


“I recognize that in the 26 years I’ve been on the air there’s probably never been a day when someone said, ‘Do you love NBC today?’ ” he said. “It’s a very long-term, very, very profitable business relationship, and 95 percent of the time our goals are the same. The other 5 percent of the time the network has its own agenda.”


Bob Greenblatt, chairman of NBC Entertainment, said he and Mr. Wolf discussed his branching out beyond “Law & Order. “I said to him, ‘You’ve obviously done all the versions of ‘Law & Order’ anyone could imagine, and that’s been brilliant and long going, but it’s time to move into a different franchise,” Mr. Greenblatt said.


“Chicago Fire,” an ensemble drama pitched to NBC as “ ‘E.R.’ in a firehouse,” is the result of those discussions. The show has continuing story lines, like the fallout from a paramedic’s accidentally plunging a needle through a girl’s heart and a rookie’s adaptation to life in the firehouse. But each episode also has plots neatly resolved after 42 minutes.


“This is one of our more character-driven shows,” said Peter Jankowski, an executive producer on each “Law & Order” iteration and on “Chicago Fire.” But he added: “I feel strongly that there’s always a place for procedurals on TV. Part of me thinks ‘Law & Order’ died an early death.”


Mr. Wolf said he didn’t have to venture too far from his preferred brand of storytelling to keep the network happy. He has worked with NBC since “Hill Street Blues” in the mid-’80s, through several owners and many different network chiefs, and he said he understood that tastes change depending on who is in charge. Mr. Greenbatt tends to prefer serialized dramas like the musical drama “Smash” and the apocalyptic sci-fi series “Revolution.” Even “SVU” more frequently uses story lines that stretch across episodes without venturing too far from its standard crescendo.