BURBANK, California: Remember when “Chuck” was a show about a helpless newcomer maneuveuring ineptly

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through a world of espionage and danger? Ch­erish those memories.

A few weeks ago, Zachary Levi, the actor who plays the nebbishy title character on that NBC show, was on a soundstage on the Warner Brothers lot here preparing to film a scene for a coming episode. Having sneaked into the secret lair of an evil spy organization, the heroic Chuck Bartowski was about to exchange gunfire with a sinister enemy agent, disarm a second bad guy with a series of kicks and punches, and knock out a third with a single blow.

What were we saying before about nebbishy?

For the intensely loyal but perilously small “Ch­uck” fan base, the scene is indicative of a new creative direction that this action-comedy series has adopted as it begins its third season. (Its two-hour premiere is on Sunday, before it moves into its traditional Monday night slot.)

It is just one of many aggressive, potentially dangerous steps the “Chuck” producers have taken to keep the show alive on a struggling network and on one of the most competitive nights of the week, knowing that it still might not be enough. “There’s a lot of perks to doing this show, but being sure of your future has not been one of them,” said Josh Schwartz, a co-creator of Chuck.

The show, following the adventures of a computer nerd with a spy database embedded in his brain, has been an embattled series since its 2007 debut. Though the show started with critical praise and decent ratings, its freshman season (which averaged nearly 8.7 million viewers) was cut short by the Writers Guild of America strike.

In its second year, a heavily promoted 3-D epi­sode shown after the Super Bowl did not stave off a declining viewership (it averaged nearly 7.4 million for the season, but 6.11 million tuned in for the season finale), and by the spring, NBC was unsure if it would renew the show.

To obtain that third-season go-ahead, Schwartz, the show’s co-creator Chris Fedak and its executive producer McG (the director of “Terminator Salvation”) met with NBC to pitch a new storyline: Via an upgrade to his brain, Chuck gains new spy abilities and physical prowess that he must to learn to control; under the right circumstances, the wimp becomes a warrior.

Yet when NBC announced its first round of fall pickups, “Chuck” was not on that list. NBC executives said they wanted to find a way to bring “Chuck” back. So the “Chuck” producers rallied every influential fan they could find, talking to popular television blogs and traditional news media outlets about the show’s uncertain status. More awareness — and more bu­zz — was generated by a web campaign started by a fan named Wendy Farrington, who encouraged others to buy sandwiches from Subway when the season finale of “Chuck” was broadcast. Ultimately, Subway may have saved Chuck when it stru­ck a sponsorship deal for the show’s third season, helping to offset the thousands of dollars that producers agreed to cut from their per-episode budgets.