Jeff Zucker was a fearless news producer and fast-rising entertainment executive who was just 41 when he became head of NBC Universal. But in the last few years, the onetime whiz kid behind the “Today” show -- he turned Katie Couric into a star -- has made several costly miscalculations that have led to a spectacular fall by the country’s premier television network.

Zucker’s troubles were magnified this week when, with NBC facing a revolt by affiliate stations furious over their sinking ratings, he decided to move Jay Leno back to late night after less than four months. The unusual measure was an acknowledgment that Zucker’s gambit to shift the comedian into prime time had failed.

NBC’s Leno flip-flop, which is shaping up to be one of the biggest debacles in television history, underscores how Zucker, who views himself as a maverick and a champion of change, now faces a decidedly different legacy. Instead of the mogul with moxie who transformed television -- he called for “a re-engineering of our businesses from top to bottom” -- Zucker might better be remembered as the guy who plucked the peacock.

How Zucker found himself in such a fix is a study in how a chief executive, confronting wrenching changes to his business, reacts to challenges.

Now the network is bracing for more fallout: Will Conan O’Brien, who last spring became host of the storied “Tonight Show,” leave the network when Leno moves from 10 p.m. back to 11:35 p.m., which could happen as soon as March? Will Leno remain content with a half-hour show, signing off at 12:05 a.m. to make room for O’Brien, if he stays? And how will NBC plug five hours of programming each week in Leno’s vacated time slot?

Some veteran TV executives believe the Leno imbroglio could ultimately cost more than $200 million, including the damage inflicted on stations’ local newscasts, their ad rates and NBC programs, such as “Law & Order: Special Victims Unit,” which lost millions of viewers when its time period was changed. They predicted that it could take years for NBC to rebuild.

“Everything about this decision seems to have been a disaster,” said Jeffrey Cole, director of the Center for the Digital Future at the USC Annenberg School for Communication. “It looks like NBC shot itself in the foot, the arm, the neck -- and everywhere else.”

Zucker declined to be interviewed. A senior NBC executive defended Zucker, saying, “I think Jeff’s legacy will be that of an innovator who was not afraid to take risks. Not all big swings will work, but many will. For those that don’t work, you have to be smart enough to know when to make a change, and that is what he has done.”

For much of his career, the 44-year-old Harvard graduate has been the master of the quick fix. Not enough hit shows on the profitable Thursday night? “Supersize” the sitcoms “Friends” and “Will and Grace” to 45 minutes. Don’t want to lose Jay Leno to a rival network? Give the late-night comedian his own show at 10 p.m. That way, NBC could keep both Leno and O’Brien in the fold.

But while Zucker’s facile management technique was suited for running a news operation, it’s had different consequences on the entertainment side of the network, which Zucker took over a decade ago.

The implosion of NBC’s prime time -- and potential damage to a TV institution, “The Tonight Show” -- can be traced to three major decisions: In 2004, assuming that the wry host Conan O’Brien was the future and Leno would be ready for retirement, Zucker agreed to give O’Brien “The Tonight Show” in 2009. At the time, it was a major coup for Zucker, the network’s programming chief who was angling to be the next CEO.

But as 2009 approached, Leno continued to triumph in the ratings and was showing no signs of slowing down. He groused on his show about his upcoming retirement, taking his unhappiness public.

Another blunder was when Zucker abruptly fired programming chief Kevin Reilly to hire the brash but inexperienced TV producer Ben Silverman to run NBC. The network quickly discovered that Silverman wasn’t cut out to be an executive, but instead of easing him out, Zucker staunchly defended him for two years. Silverman created management turmoil and a string of duds that cost the network hundreds of millions of dollars.

Finally, in December 2008, Zucker, fearful of losing a disgruntled Leno to rival ABC, wooed him into prime time, clearing the “Tonight Show” perch for O’Brien. People close to Zucker said the decision was prompted by Zucker’s desire to keep Leno at NBC and keep his 2004 promise to O’Brien.

Associates said Zucker boxed the network into an untenable position because of his tendency to focus on short-term gains and concern for perception. In his eagerness to keep Leno and O’Brien from defecting to rival networks, he failed to anticipate the collateral damage a low-rated 10 p.m. show would inflict on the newscasts of NBC affiliates.

“I think Jeff is a brilliant marketer and a brilliant tactician and a terrible strategist,” said a former NBC executive who works in the TV industry and did not want to be named criticizing Zucker. “His view is, give people what they want at the time they want it. He’s not a long-term strategy guy.”

Still, while Zucker’s retreat on Leno may be embarrassing, few seem to think it will lead to his immediate ouster. For one, General Electric signed a new three-year contract with Zucker in December, and no changes are expected until after NBC Universal’s merger with Comcast Corp. closes.

“The amazing thing about Jeff Zucker is nothing bad ever seems to stick on him,” said Ethan Heftman, vice president and director of national broadcast at the ad buying firm Initiative. “He has a knack for whatever happens program-wise, he’s able to deliver a level of profitability that appeases his bosses. This is certainly a bigger deal than other things that didn’t work.”

The network still may be able to reverse its fortunes if it uses the opportunity to reboot its prime-time lineup, television industry executives said.

“It could be the silver lining in a season of dark clouds in that the network gets to start fresh with a creative and scheduling blank slate, which may be an unprecedented prime-time opportunity,” said John Rash, senior vice president and director of media analysis at the Minneapolis-based advertising firm Campbell Mithun.

Indeed, TV writers who were dismayed when NBC turned the 10 p.m. hour over to Leno welcomed the notion that the network might once again be shopping for new programs.

“I think we’re all relieved,” said veteran writer Tom Fontana, who has produced shows such as “St. Elsewhere” and “Homicide,” as well as last season’s “The Philanthropist.” “We’re going to get five hours of real estate back that we lost. I’m thrilled that NBC will be back in the drama business.”

meg.james@latimes.com

matea.gold@latimes.com

Times researcher Scott Wilson contributed to this report.