This must be it. Monday morning. Los Angeles. The 20th Century Fox lot. A little bungalow in the corner. Unmarked, hard to find. One of the writers here is leaving for the day: A mysterious computer virus has invaded his machine, nobody can track it down. A casting director enters. Says one of his two dogs inexplicably disappeared from his locked house over the week-end, then reappeared at the back door 36 hours later.

Yeah, it makes sense that this is where they put together “The X-Files”. The Friday night show is Fox TV’s underhyped successor to “The Outer Limits,” “Kolchak:The Night Stalker,” “Twin Peaks.” Strange things happen in the Northwest woods, in the Nevada desert, in government corridors. Two FBI agents poke around. One of them, Fox “Spooky” Mulder, believes in the paranormal, expects to find an alien in every clost; the other, Dana Scully, thinks Mulder’s nuts and looks for scientific explanation.

This is not normal TV: Most of its episodes end in uncertainty, with Mulder and Scully-and us, for that matter- learning little but falling far short of the big picture. Also, the show has broken the primetime rule that says any two attractive but antagonistic co-workers are thrown together, sexual tensions will rise, they’ll sleep together, and the show will go down the tubes.

As usual for Fox shows, the ratings haven’t been great, but a focal, demographically desirable group of mostly 18-to-49-year-old males helped the series overcome a slow start.

“I think we might have been overlooked at first,” says Chris Carter, the show’s creator and co-executive producer. “People are always looking for that big, explosive hit, but not a lot of people watched us at the beginning. And people don’t always take Fox seriously. It’s been the network of “Married…With Children,” “Studs,” and “90210,” and people have had to change their mind-set to accept something like “The X-Files”.”

Among those who had to change were the actors. Anderson, 26, began acting off-Broadway, then moved to Los Angeles- “swearing,” she says, “that I would never audition for a TV show.” She laughs. “But being out of work for a year changes your mind.”

For his part, Duchovny, 34, whose resume include “Chaplin,” “The Rapture,” “Twin Peaks” and Showtime’s “Red Shoe Diaries” (not to mention a stint as a Yale grad student), read “The X-Files” pilot, liked its combination of humor and macabre drama and say it as “a good one-hour movie and maybe a few episodes.” Later, he realized that it might have more staying power than that. “I thought it was just a show about extraterrestrials,” he admits. “But once it opened up into the area of anything paranormal, I could see that it need not ever die.”

Indeed, the series has inspired a “Star Trek”-like cult. Devotees of the show flock to computer bulletin boards on such services as America Online and Prodigy, where these self-named “X-Philes” create detailed character backgrounds, compile arcane, astonishingly detailed fact sheets, speculate on a Mulder-Scully romance (about which the consensus seems to be a resounding NO, as long as neither of them gets involved with anyone else), and just voice their opinions: “Mutants OK, but NO vampires on “X-Files”, please. Especially if they’re played by Tom Cruise.”

“The X-Files” folks are well aware of this: Carter used to read up to 70 pages of downloaded fan comments each night, while in a recent on-line forum co-executive producer Glen Morgan said certain shows had been tailored to please the modem squad.

And while the actors aren’t quite so computer literate, they are aware of the attention. “I’ve been told that on one of the computer services there’s something called the Gillian Anderson Testosterone Brigade,” says Anderson with a laugh. “That just tickles me.”

This season, Anderson would like the characters to become more emotionally involved in their cases, though she knows that the show needs to maintain a certain degree of detachment. (As does she: “This is pretty gruesome stuff that we deal with, and I have to underplay it so that I don’t have nightmares.”) Duchovny wants to add more humor, and Carter just wants to deal gracefully with Anderson’s maternity leave (she’s married to an art director). For now, Mulder will have a new partner.

Carter is also trying to handle the demands of a show whose cult seems to be expanding. “The tone of this show is subdued and subtle,” Carter says, “and I never expected fan clubs and T-shirts and all of that. I think the show should remain dark and cultish.” He grins. “Everyone should *watch* it, of course, but it should be still dark and cultish.”