Indie film wouldn’t exist as it does today if it weren’t for the actors who give their names — and their back-end — to make these movies possible.

The benefits are mutual. While non-studio projects get financing, publicity and award-season traction, A-list talent gets to take a break from performing in green-screen limbo and deliver the kind of fierce dramatic moments on screen for which they were trained.

Every few years, the independent industry seems to cultivate a fresh crop of top actors who dabble in Hollywood while staying true to their indie roots. Among the women, Nicole Kidman, Frances McDormand, Julianne Moore, Tilda Swinton, Catherine Keener, Maggie Gyllenhaal and Michele Williams are the biggest names working in both worlds. On the men’s side, there are Jeff Bridges, George Clooney, Brad Pitt, Philip Seymour Hoffman, Sean Penn, Woody Harrelson, James Franco and Ryan Gosling, among others.

They are the thespians who keep indie film vibrant — and bankable — not to mention offering Hollywood’s tentpoles a dose of prestige when they need it.

Historically, independent film financing was based on foreign and video pre-sales “driven by the presence of washed-up TV actors who could move videoboxes,” says Focus CEO James Schamus, remembering what he fondly calls the “Vestron era” — so named for the independent shingle of the mid-to-late 1980s that released such titles as “Hot Pursuit,” “And God Created Woman” and hit with “Dirty Dancing.”

“To some extent, that history continues to this day in terms of the calculations done on the value of cast,” Schamus says.

However, he adds that today there are no set numbers. “The biggest star in the world, who gets paid $25 million, doesn’t increase the value of a $1 million to a $25 million movie,” he says.

What a well-tested actor can do, Schamus and others in the industry point out, is give credibility to a project. “Great stars bring it on,” he says, “and that does create value. But it’s actually quite subtle.”

But Cross Creek’s Brian Oliver, a producer on “Black Swan” and “Ides of March,” disagrees. “The international marketplace is definitely still star-driven. There’s probably 15 guys and 10 gals that can actually carry a movie on a certain budget in the foreign marketplace,” says Oliver.

In the case of Cross Creek’s “Ides of March,” the film had the good fortune of having both Clooney and Gosling on board. Without them, Oliver concedes, a movie like “Ides” wouldn’t happen.

“The reality is there’s a model that you have to put together to make these movies without a studio, and the model requires pre-sales, so none of these movies would have been made had they not had a movie star involved,” he says.

Gosling, whose status has risen in the last year not only with with “Ides” and Warner Bros.’ “Crazy Stupid Love,” also helped make Nicholas Winding Refn’s Cannes player “Drive” a reality. Producer Marc Platt says he was able to get the film financed by Bold Films and Odd Lot Entertainment on the basis of the script, the actor and the director. “Ryan is one of the great actors of his generation,” says Platt. “And he put the stamp of quality on it.”

“Drive” also has the benefit of an inspired supporting turn by Albert Brooks, who offers that uniquely indie experience of a well-known actor breaking out of the designated box — think Charlize Theron in “Monster” or Jim Carrey in “Eternal Sunshine of the Spotless Mind.” “We always love actors taking unexpected turns,” says Platt.

Gosling was also far more involved in the making of “Drive” than a standard hired player on a Hollywood project, helping to bring Refn on board the project, chauffeuring the filmmaker around L.A., finding locations and collaborating on the character.

It’s a testament to how much actors bring to indie projects, beyond the level of a performance.

As producer Lawrence Inglee says, “It takes so many people to get a movie made that goes against the grain of the business, so they’re playing a role that isn’t just the role of star or actor; it’s a wide reaching collaboration, and the movies couldn’t happen without that.”

For instance, in Inglee’s recent production of Oren Moverman’s “Rampart,” which stars Woody Harrelson as a corrupt cop, the actor and thesp-producer Ben Foster were “instrumental,” says Inglee, “in shaping the material.”

And because the team had all worked together before on Moverman’s “The Messenger,” which garnered Harrelson an Oscar nomination, Inglee says, “There was an intimacy and shorthand that existed on set that was invaluable.”

For Harrelson, independents have been his “favorite movies” to do, he says.

“And they have also been the most enjoyable ones to work on.”

And like many of his brethren in the business, Harrelson prefers to do roles that challenge him. “I make decisions based on the material and the content, not the financial reward,” he says.

Tilda Swinton has also frequently gone to bat for indie projects, going above and beyond the call of simply being a performer in a project. Being an actress, she says, “is something I spend far less of my life concentrating on than the practical business of drumming projects into life.

“It is a rare holiday for me to work only as a performer on a film,” says Swinton, who helped make last year’s Italian-language indie “I Am Love” (for which she was also a producer) and Lynne Ramsay’s latest “We Need to Talk About Kevin,” for which she committed to early; she also deferred her fees.

“I would call myself a filmmaker, just as anyone who helps to make films might,” Swinton adds.

For further proof of high-profile thesps’ dedication to indies, this year we’ve also seen Williams’ transformation into Marilyn Monroe in “My Week With Marilyn,” Clooney (again!) tough out the death of a spouse in “The Descendants,” and Kate Winslet toss her cookies in “Carnage.”

But not everyone believes actors are the key to the viability of indie film. “Frankly, I’m appalled that this is how we put movies together,” says veteran producer Ted Hope, whose most recent pics “Martha Marcy May Marlene” and “Dark Horse” starred, respectively, up-and-comers Elisabeth Olsen and Jordan Gelber.

Casting name actors may give the appearance that a project is mitigating risk, “but,” says Hope, “tell that to the investors of that Nicolas Cage-Nicole Kidman thriller.” (The film “Trespass,” a thriller distributed by Millennium Entertainment, tanked in theaters, grossing only $24,000).

In today’s world of “superabundance and access,” says Hope,” with “more movies that you could ever consume and available in more places than ever before, there’s no such thing as quantifiable economic indicators — which is what actors were.”

As James Schamus says, “(Indie film) also has an execution-dependent history. At the end of the day, if the movie isn’t good, it doesn’t matter if it is jammed full of movie stars.”