Mondo documentaries that show up on channel 82 when Mom thinks you're asleep. No-budget horror flicks filmed in Boise. Drive-in biker swill that gives impressionable teens a richly misleading education in sex and drugs. You're not supposed to admit you even saw these movies, let alone enjoyed them. Such fringe detritus is the forgotten dreck of filmdom.
Michael Weldon remembers, though, and he's done something about it: He has become a one-man cottage industry devoted to movies so weird they're mesmerizing. He calls them ''psychotronic films'' (''psycho meaning the horror film and tronic suggesting science fiction''), and his essential 3,500-entry Psychotronic Encyclopedia of Film gives cinematic cheese like The Gore-Gore Girls and Mondo Daytona their due. Keeping the flame fanned is a quarterly fanzine, Psychotronic Video, Weldon's rolling vault of horrors, nudies, teen pics, and such subgenres as ''Sick '70s Movies by Guys Named Curtis.''
''I don't call them bad movies,'' Weldon says, ''though a lot of them are bad, including some of my favorites.'' The 39-year-old editor cultivated his democratic approach in Cleveland's long-gone movie palaces and drew inspiration from a former TV-horror-movie host named Ghoulardi. In 1980, after moving to New York, Weldon started a weekly guide to trashy TV fare, and in 1983 Ballantine published the Encyclopedia (a second volume is due next fall from Pharos). Now the banner that fell with the demise of the B-movie house has been picked up by video, and Weldon leads the crusade. Every three months, fans the world over (outside the U.S., the magazine does best in Berlin) can read about ''Christopher Plummer in Canadian Drug Movies'' and ''British Vampires With Avengers Stars.''
''Each month new things come out that amaze me,'' Weldon says. ''Obscurities from all over. There are interesting, even good, movies just sitting in warehouses or somebody's closet.'' Never fear that many tapes won't make it to your corner store. ''Sometimes it's work to find these things, but there are sources. If you can get it, I'll print how.''
That ain't the half of it. In its 10 issues to date, Psychotronic Video has become something of a university without walls. The video reviews range from forgotten classics to garage-made shorts, the obits note the passing of cult faves, interviews take on the likes of Clive Barker and James Coburn, and letters present an ongoing scholarly dialogue (''You confuse two different 1973 Autopsy films,'' writes one diligent reader).
Weldon's own expertise has led to stints as a host of psychotronic-film festivals here and abroad. His latest enterprise is the Psychotronic Store in New York's anarchic East Village, co-owned with his wife, Mia, a dress designer. It stocks 1,000 tapes, the 1992 Psychotronic calendar, posters, and lobby cards. Weldon dreams of running a theater someday, but his primary goal remains to get the movies he loves seen however he can. ''I'm just trying to turn people on to these incredible films,'' he says. Some so incredible they should only be risked in the privacy of your living room.