WHEN Jared Hess, best known as the director of ''Napoleon Dynamite,'' was in Mexico City casting ''Nacho Libre,'' a new comedy in which Jack Black plays a priest in training turned wrestler, he auditioned a number of real-life wrestlers, who showed up wearing colorful masks.

Naturally, Mr. Hess asked them to remove their disguises. But they all refused.

And he thus learned the first rule of Mexican wrestling, known as lucha libre (literally ''free fight''): Iconography is everything.

''We learned very quickly that asking them to remove their masks was too much,'' said Mr. Hess, whose film opens on June 16. ''There's a lot of integrity in that.''

Integrity is only part of it. Considered kitsch by some, a unique cultural phenomenon by others, masked wrestlers have been popular in Mexico since the 1930's, when an American promoter introduced the concept south of the border. Because masks played a ceremonial role in pre-Columbian Indian cultures, the disguises went over especially well. Today their wearers embody a combination of average Joe and working-class avenger.

''The lucha mask is a symbol of strength and empowerment in the Mexican and Chicano culture,'' said Michelle Martinez of the Department of Chicano Studies at Arizona State University. ''The mask goes back to Aztec and Mayan times, and also brought the luchador to the superhero level. It gave them this larger than human appeal.''

The lucha culture spoofed in ''Nacho Libre'' approached its peak in the 1950's with the ascendancy of El Santo, el Enmascarado de Plata (Santo, the Silver Masked Man), the greatest star of the Mexican ring. Santo, whose real name was Adolfo Guzman Huerta, became a sort of Everyman hero who stood up for the rights of the oppressed. He starred in comic books and more than 50 movies, and because he never removed his mask -- either in his films or in public -- he remained a mysterious figure even in death. (Guzman Huerta, who died in 1984, was buried in his headgear.)

Other luchadores, with names like Blue Demon and Mil Mascaras (Thousand Masks), followed Santo to the silver screen, and from the 50's through the 80's they appeared in numerous films, battling everyone from Dracula and the Daughter of Frankenstein to the Mummies of Guanajuato. With their cheap production values, clich?idden dialogue and barely competent performances, these films make it look as if Ed Wood had a secret career in Spanish-language pulp. But they were enormous successes at the time and gave Hispanic children their own cinematic role models.

''They can be dismissed as sort of low-end rip-offs of other genre films made in America,'' said the Mexican director Guillermo Del Toro, whose latest work, ''Pan's Labyrinth,'' opens this year. The movies have a ''surreal logic to them,'' he said, ''and sometimes they achieve almost a dreamlike quality. There is a zany, non-Anglo sensibility that is less sophisticated, but far more charming in many ways.''

Lucha bears only a passing resemblance to the arena rock stylings of American pro wrestling. Although they both have heroes and villains, and many of the rules are the same, the audiences and symbolism are entirely different. In lucha, occasional matches involve masked wrestlers who bet their disguises. If one can unmask the other, the loser must reveal his true identity. And the longer a luchador defends his mask, the higher his status in the ring. There are also matches in which the loser is forced to shave his head, a symbolic moment in the land of machismo.

Lucha libre is ''a family event,'' said Mike White, one of the screenwriters of ''Nacho Libre.'' ''When you go to these matches, you see little kids to old ladies. It's a community event, not just for teenage boys.''

In recent years lucha has also become an example of rasquachismo, an essentially indefinable term that describes underdog art containing elements borrowed from other cultures. As an illustration, Professor Martinez mentioned a luchador whose headgear features Aztec and Louis Vuitton designs. There are also luchadores who perform under names like Destructor Nazi (complete with swastika armband), Robot R2 and Ultraman. ''Lucha,'' Professor Martinez said, ''is really an assemblage of a lot of international influences, but the ritual that goes along with it is very Mexican.''

That essential Mexican identity has not stopped American hipsters from latching onto lucha style and adding their own little touches. There are fanboy-oriented lucha Web sites like frompartsunknown.net; several rock bands perform wearing lucha masks; stitching patterns for lucha head gear can be ordered over the Internet. There's even a lucha noir novel called ''Hoodtown,'' and at least two children's cartoon shows, ''Mucha Lucha!'' and ''Ultimate Muscle,'' have featured lucha performers. Then there's Lucha Va Voom, a touring show of wrestlers, comedians and burlesque that seems to be a convergence of rasquachismo and camp.

''Nacho Libre'' borrows its inspiration as well, some of it from historical sources. A 1963 Mexican lucha movie called ''El Se?Tormenta'' told the story of a priest who becomes a luchador in order to save his orphanage. The film encouraged a real priest, the Rev. Sergio Gutierrez Ben?z, to take up wrestling in order to save a shelter for homeless children in the port city of Veracruz. Fighting under the name Fray Tormenta (Brother Storm), he appeared in more than 1,000 matches and raised enough money to shelter more than 3,000 street kids. (A similar story was told in ''The Man in the Golden Mask,'' a 1990 French film starring Jean Reno and Marlee Matlin.)

Mr. Hess, who said he had seen several Santo movies in college and was ''blown away by the aura and mystique surrounding luchadores,'' heard about Fray Tormenta several years ago. When the opportunity arose to make a film about lucha libre, he said, ''I jumped at it.''

Mr. White added: ''Those movies brought Jared to the edge of giddy rapture. It seemed like this was an untapped place to draw comedy from.''

Whether ''Nacho Libre'' will plug into negative Mexican stereotypes is another matter. Lucha may appear to be pop culture kitsch, but its adherents take it seriously. Lourdes Grobet, whose decades-long love affair with the sport culminated in ''Lucha Libre: Masked Superstars of Mexican Wrestling,'' a book of her photographs, said that anyone who thinks lucha and the lucha films are camp is indulging in ''a social class prejudice.''

Richard Montoya, an actor who appears in the film and is also a member of the Chicano performance-art group Culture Clash, said he believes Mr. Hess ''applied his smarts to this'' and ''found an uncanny way of staying clear'' of stereotypes.

''I think a lot of Mexicans will find the real Mexico in this film,'' Mr. Montoya said. ''Besides, it seems every time a Mexican puts on a mask, it changes the world. Zorro wore a mask. Subcomandante Marcos wears a mask. There seems to be something Mexican about the individual who dons the mask but represents the masses.''

Photos: A number of masked wrestlers went on to become movie stars in Mexico, among them Blue Demon, top, and El Santo, el Enmascarado de Plata (Santo, the Silver Masked Man), seen here in ''Santo vs. the TV Assassin.'' (Photographs by Lourdes Grobet, from the book ''Lucha Libre: Masked Superstars of Mexican Wrestling''/D.A.P.); Jack Black, left, as a priest in training turned wrestler, with Hector Jimenez in Jared Hess's ''Nacho Libre.'' (Photo by Daniel Daza/Paramount Pictures)