SOMETHING WAS NOT RIGHT.

There I was, touring the FBI Building on a cold December morning, lurking in the midst of unsuspecting Nikon-toting visitors. I was looking for any trace, any acknowledgment of the most popular TV portrayal of the Bureau these days, Fox's "The X-Files." I wasn't making much progress -- but I was finding plenty of grist for the conspiracy mill.

First, I kept setting off the metal detector at the entrance -- just like the episode where FBI agent Dana Scully discovered a computer chip implanted in her neck. (This made me a little anxious.) Then came the displays along the tour about the FBI's "priorities": plenty of info on things like bank fraud, insurance fraud, health care swindles, but nothing on hunting down extraterrestrials. (Coverup!)

One wall was lined with posters from 1930s gangster movies, others featured a shot from "The Silence of the Lambs" and the logos of "America's Most Wanted" and "Unsolved Mysteries," but nowhere could I find any reference to a certain Friday night drama or its lead characters, agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson). (Denial!)

What do the folks at the FBI really think? Curious, after the firearms demonstration I asked Special Agent Peter Georgacopoulos about the show. "People ask with the utmost seriousness if the FBI has X-Files," he said. "I usually explain with the utmost seriousness that I'm the case agent for extraterrestrials."

Aha -- proof! But seriously, Georgacopoulos says he likes "The X-Files": "{Agents Mulder and Scully} are sensitive to the needs and concerns of these people, that their neighbor's head's exploding or whatever."

Well, it wasn't quite what I was looking for, but it would have to do. Things tend to work like that when you're dealing with a show devoted to detailing messy government conspiracies -- as I found out later that afternoon.

"The X-Files" may be just another series, just a flickering arrangement of brightly colored dots on your TV screen, but it's also the source of one of the richest fan cultures around since "Star Trek" -- one whose plot has touched down in the Washington area many times.

Just like Tom Clancy fans can note that the Mitre Corp., described in Jack Ryan novels as a CIA-front company, can be found right here in McLean, fans of "The X-Files" can enjoy all sorts of local color. Even though it's filmed in Vancouver, the show has taken us across and around the Washington area, from Georgetown to Germantown, as revealed in lines of dialogue, on-screen details and those location-setting bits of text at the start of scenes ("FBI Headquarters, Washington DC, 8:45 a.m."). We traced a few of these settings across the real map of the D.C. area, discovering, among other things, that northern Montgomery County is a much stranger place than it's normally given credit for.

For that, you can blame series executive producer Chris Carter's past travels -- "these {settings} are places I've usually been to," he said in an interview. And you can blame Carter's brother. "My brother used to live in Germantown and work in Gaithersburg," he explains, when asked about a succession of northern Montgomery settings. Carter's brother now lives around Kalorama, entirely uncoincidentally the location where the show's creator places FBI agent Scully's apartment.

Fans of the show find this sort of trivia both intriguing and annoying..

Mike Holmes, a student at the University of Maryland at College Park, noted the series of episodes about a slithery human-liver-eating mutant, Eugene Tooms, residing at "66 Exeter Street" in Baltimore: "I was curious about it, though, and looked at a map to see if there really was an Exeter Street -- there is!"

Then there's the other extreme: "Only a few external shots have been clearly identifiable as Our Town rather than recycled Vancouver," viewer Colin Alberts, a lawyer in Arlington, said via e-mail. "It can get laughable. . . . The Senate Office Building' external shot they show for a lead-in to meetings with Senator Matheson' (who I think is clearly modeled after Claiborne Pell, even before this DIA psychic story broke) looks nothing like any of the real things."

Upcoming episodes might be a little more realistic. Carter mentions wanting to ship out a crew to shoot footage around the Vietnam Veterans Memorial and the Library of Congress, and alludes, somewhat mysteriously, to "a list of scandalous sites here that I've been wanting to draw from. I've got a nice little book here, Scandalous Sites of D.C.' "

What would inspire someone to pull out a Baltimore map and double-check a location fleetingly mentioned in a fictitious and entirely implausible television program? Well, there are X-Files, the fictitious, unsolved FBI cases at the heart of the show's plot, and then there are X-Philes, devotees of the series. Like Trekkers and "Star Trek," X-Philes are a dedicated lot when it comes to the workings of their show.

And those workings get quite complex, as, week after week, Mulder and Scully try to unravel a tangle of paranormal oddities, government conspiracies and various gruesome crimes. As fan Alberts elaborated: "Any show that contains the symbolic and conspiratorial qualities of The Prisoner,' the bizarre aspects of Kolchak: The Night Stalker,' the offbeat humor and creepy film noir taste of Twin Peaks,' AND the presence of Gillian Anderson, is a show I'll set my VCR for."

One of D.C.'s biggest employers is, of course, the military-industrial complex, and the show has drawn a substantial following there -- ironic given its emphasis on coverups and conspiracies originating "at the highest levels," as they say. What's it like to be one of the people most likely to be a witting or unwitting participant in one of these cabals?

"I just don't give the government enough credit to hold together such an elaborate conspiracy for so long," e-mailed David Wiesenhahn, an analyst working at a defense think tank in Alexandria. "I think I formed this opinion after I moved here five years ago and started actually meeting the people that would be carrying out this conspiracy."

In the finest American tradition of milking a good idea for an extra buck or two, "The X-Files" has already spawned a series of spinoffs -- comic books, three novels, an official handbook, trading cards and more posters, T-shirts and coffee mugs than the FBI could count. Stop by the Another Universe store in Georgetown, and you'll see shelves lined with the stuff, right next to the "Star Wars" action figures and the "Star Trek" books.

"If it gives you any idea, X-Files' is a category on my budget," Mike Hernandez, a student at the University of Maryland in College Park, said in an e-mail message. "If an article appears in a magazine, or newspaper, on any of the actors/actresses or even the show itself, I quickly grab it from the store. I own the X-Files' books, posters, and have magazine clippings on my wall, as well as the 1996 X-Files' calendar. . . . I have also made it a point to acquire all the comics. . . . Friday nights are strictly reserved for the X-Files,' and since the purchase of my VCR, I now record all the shows, and late-night talk shows that the actors appear on (at least when I get a chance)."

When we asked Chris Carter what he thought of that sort of appreciation -- half expecting to get a response like William Shatner's "get a life" line in a Trekkie-tweaking "Saturday Night Live" sketch -- he insisted that it's what he wanted all along.

"This is the kind of fan and following you hope for," he said. "I think there's a tendency to believe that the writers or producers have a disdain for their audience, particularly people who take it that seriously. {But} it's not like the crazies have come out of the woodwork and we're trying to hide from them."

Actually, some of the crazies -- the ones in the show -- have come after the fans, so to speak. Last weekend, the Georgetown and Baltimore Another Universe locations hosted one of the stranger guest stars of the series, Doug Hutchison, who played Eugene Tooms in three first-season episodes. More than 500 people showed up for the autograph-signing and picture-taking at each location.

But most X-Philes seem to meet not in person but on-line -- appropriately enough for a show this conspicuously high-tech (Mulder and Scully seem to have their cell phones surgically attached). One "X-Files" Usenet newsgroup, or electronic bulletin board on the Internet, alt.tv.x-files, sees more than 100 new postings a day. There's another discussion ongoing via an e-mail list, major fan forums on America Online and Delphi, and dozens of World Wide Web pages on the show, the stars and such supporting characters as FBI Assistant Director Walter Skinner (Mitch Pileggi), Mulder and Scully's tightly disciplined boss.

Like much on-line discourse, X-Philes' conversations are bewildering in both their knowledge and their inanity. People pick up on the smallest things -- "When Mulder shows Scully the pictures of Japanese medical experiments, they have top secret' in Japanese kanji in the lower right-hand corner," noted one observant viewer recently.

Many of the participants bring some rather specialized expertise; after one episode this season featured an FBI technician scraping data off a reformatted computer disk, several people wondered how that could be done. Several mini-dissertations on data security ensued, such as this explanation of federal government standards for securely erasing disks: "A degausser must be able to reduce a test signal on the type of media by 90 decibels, or to 109 of its original strength."

But since this is Usenet, possibly the world's least organized information resource, there's also an abundance of recurring questions (like, what kind of gun do Mulder and Scully use?), arguments in search of irrelevance (was David Duchovny cheated or not when he lost on "Jeopardy!"?!) and gratuitous, poorly couched insults: "Speaking of stupidity, try concealing yours a little better in the future."

Warns longtime fan Sarah Stegall: "The newsgroup is the last place to go for accurate information. The place is crawling with trolls and nut cases, and is a mine of guesswork, speculation and just plain misinformation." Stegall, who researched the official guide to the show, suggests that fans new to all this try the mailing list (see the box for details on this and other on-line resources).

Carter and other writers for the show try to keep up with this chatter; several shows have used the names of on-line X-Philes for guest characters, and many plot elements seem written as a direct response to comments on-line. The Lone Gunmen, a trio of conspiracy theorists who occasionally advise Mulder and Scully, were created by writers Glen Morgan and James Wong in the first season in response to some of the more obsessive triviology: "All of us had felt the various bruises and scrapes of the nit-picking," Carter said. "We actually pay quite a bit of attention. Sometimes when there's enough voices out there, we'll actually try to include a little bit with a joke in it."

Like, say, the Lone Gunmen's invitation in one episode to Mulder to join them on the Internet for a Saturday night spent "nit-picking the scientific inaccuracies of Earth 2.' " Mulder's response? "I have to do my laundry."

Speaking of dirty laundry, there was still the matter of the FBI's response. I had talked to the tour guide for a few minutes, eventually leading him to mention something about not wanting to be put "in a funny spot" speaking for the FBI. He said he didn't feel comfortable speaking with me without checking with his superiors. Uh-oh.

The call came later that afternoon. Shortly after I returned from the tour, a Bureau spokesman left a message on my phone. I phoned him back, and, after a few short questions about what I was writing about, he intoned, "I'm sure that they told you that there are no X-Files." A few words of goodbye later, the line went dead.

The truth is, still, out there. X MARKS THE SPOT

Loyal "X-Files" viewers know that Washington and its suburbs are routinely erupting in unexplained phenomena. And that it's the home base of agents Fox Mulder and Dana Scully and the agency they work for/against. Consider this a map of their stomping grounds. We even managed to pin creator Chris Carter down on where he thinks our heroes live (which we found contrasted with many fan's expectations, oddly enough). Never mind that a young, unmarried FBI agent couldn't afford to live in one of Washington's swankiest neighborhoods and that there's no river and, thus, no bridge in Bethesda. The universe of "The X-Files" is as much attitude as geography, so please excuse any apparent inconsistencies. (We're pretty sure, however, that there are alien life forms in Gaithersburg.) WASHINGTON, D.C.

FBI headquarters: 10th and Pennsylvania NW. Workplace of "the FBI's most unwanted," Fox Mulder and Dana Scully, as well as assorted superiors, colleagues and such taciturn individuals as the anonymous, insidious Cigarette-Smoking Man, aka Cancer Man.

Mulder's apartment: Capitol Hill. Mulder's nondescript apartment, #42, with a window often "accessorized" with an X marked out with masking tape. Occasionally "redecorated" by often unknown, always unapprehended government agents.

Scully's apartment: Just southwest of Kalorama. Prone to frequent visits by liver-eating mutants, alien abductees and armed, anonymous agents, Apartment 35 is perfect evidence of why ground-floor apartments are a bad security risk. Maybe that's why Scully seems to move so often -- her apartment has changed location several times.

Offices of the Lone Gunmen: Southeast D.C. The three conspiracy theorists (and sometime advisers to Mulder and Scully) publish the Lone Gunman magazine from this quadrant of the District, just close enough to the halls of power to be nettlesome.

Office of Sen. Matheson: Capitol Hill. Mulder's Congressional patron and sometime informant obviously has some pull when it comes to office assignments, judging from the outside appearance of this distinguished-looking neoclassical structure. (Sure, real senators don't have separate buildings for their offices. We know, we know...)

Georgetown University Hospital. Scully mysteriously appeared here after her abduction in the second season; also where a researcher conducted some quick alien DNA tests for Mulder and Scully at the end of the first season.

Basement, Watergate Hotel. With the Watergate's checkered history, who could resist using it as a secret meeting place, as Mulder and Scully did at the start of the second season?

Kennedy Center. Another convenient meeting spot. A balcony here saw Mulder learn from his anonymous, highly placed ally "Mr. X" the whereabouts of an alien bounty hunter, as well as X's opinion of the evening's opera: "Wonderful -- never slept better."

Japanese Embassy: On Massachusetts Avenue NW, two blocks south of Rock Creek. Just weeks ago, a Japanese agent captured by Mulder in Allentown, Pa., and then let go, was executed in the backseat of a limo in front of here. MARYLAND

"Fort Evanston." Site of the havoc inflicted by a homicidal telekinetic quadruple-amputee Gulf War vet this season.

Gaithersburg. Home of the Emgen Corp., a small genetics research firm with a specialty in alien DNA until its proprietor was found hung from a window. Also where "Deep Throat," Mulder and Scully's mysterious high-level source, was shot on a bridge.

Bethesda. On a bridge here, Mulder's attempted trade of who he thought was his long-abducted sister for Scully went awry. And Scully and Mulder wound up at the U.S. Naval Hospital after being stranded on a destroyer off the coast of Norway, aging decades there as a result of drinking contaminated water.

University of Maryland: College Park. The crime labs here have been called on to support investigations several times, such as when a researcher used photo-interpretation software to detect a ghostly form leading a child onto a railroad track.

Germantown. Location of a workshop of one of several alien clones; also site of the Vacation Village Motor Lodge, where Scully incurred some room-damage charges after being attacked and kidnapped by an alien bounty-hunter impersonating Mulder. This city also figured in the first season's tale of a gender-swapping killer.

Rockville. At a women's health services clinic here Mulder encountered more of those alien clone this time, all identical to his sister, Samantha.

"Fort Marlene." Site of a high-security medical installation with a very exclusive collection of frozen alien embryos. VIRGINIA

The Pentagon. The questions of the X-Files may reside at FBI HQ, but the answers lie in a large room filled with filing cabinets deep in the bowels of this building. This same room is often used to store such curios as frozen alien embryos.

Crystal City. A would-be HAL 9000 computer ran amok in an office building here in one of the early first-season shows, reacting poorly to plans to shut it down.

North Arlington. A nondescript house on a quiet street saw some ghastly behavior with a garage door-opener, as well as strange Romanian exorcism rituals, in the second season.

Rosslyn. Earlier this season, a child playing in the backyard of a house here was buried alive by a "phantom soldier" in a cruel echo of a certain Gulf War battle tactic.

Quantico. Mulder and Scully are both alumni of the FBI's academy here, and its labs have seen duty during various grotesque autopsies. The X-Files' in Cyberspace

A weekly fix of "The X-Files" not enough? The books, calendars and T-shirts leave you wanting more? Here are the best places to get started surfing the show: USENET

alt.tv.x-files A freewheeling discussion of the show, its characters, life, the universe and everything. High-volume (100+ postings a day) and very disorganized.

alt.tv.x-files.creative Much more orderly and social, it's a place for fans to post their own "X-Files" episodes and stories. E-MAIL

To subscribe to the X-Files mailing list, send e-mail to listproc@chaos.taylored.com, with the subject line blank, and in the body the words subscribe x-files {your name}. Expect two to four digests, of 10 to 15 individual messages, each day, with, of course, more on Saturday, Sunday and Monday. WORLD WIDE WEB

"X-Files" Web pages are becoming as ubiquitous as, say, "Star Wars" pages. Start with the official site, at http://www.thex-files.com It includes episode and character descriptions, background info, contests and links to other pages. Other good places to visit:

http://www.webcom.com/munchkyn/, run by veteran X-Phile Sarah Stegall, includes thoughtful, detailed reviews of most episodes and links to more about David Duchovny than you may have wanted to know.

http://www.bchs.uh.edu/ ecantu/GATB/gatb.html is an equivalent fan site for Gillian Anderson. (That character before the "ecantu" in the e-mail address is a tilde.)

http://www.rutgers.edu/x-files/, one of the most well-established fan pages, includes the show's FAQ (Frequently Asked Questions) file.

http://aea16.k12.ia.us/ricke/netpickhome.html The "Netpicker's" guide to the show, home to insights like "I've seen a tape of an electrocution before and it didn't look like that." Rob Pegoraro writes about the Internet and electronic gadgetry for The Post's Fast Forward magazine. You can e-mail him at pegoraror@washpost.com. CAPTION: Their work takes Agents Mulder and Scully (David Duchovny, center, and Gillian Anderson) all over the country, but they always return "home" - to Washington.