NOT all of "X-Files" creator Chris Carter's best ideas go into the twisting plots of his hit TV series. Carter is also putting that famed paranoid imagination to use to keep his scripts safe from snooping eyes and thieving Xerox machines.
     On shows ranging from "The X-Files" to "NYPD Blue," protecting the plotlines of upcoming shows from falling into the wrong hands has become a huge headache - requiring a series of ever-evolving, CIA-like security measures.
     The most sought-after targets these days are pages from the final episode of "Melrose Place" and the new series Carter has created for Fox next season, "Harsh Realm."
     Once a script is leaked, it usually ends up posted somewhere on the Internet - spoiling the suspense for millions and, in some cases, costing the networks untold viewers who figure they no longer have to watch because they already know what's going to happen.
     "We had a security leak earlier this year, where someone had broken into an executive's office at Fox and gotten the advance scripts on "X-Files" and "Millennium" and published the story lines on the Internet" X-Files creator Chris Carter told The Post yesterday. "We live in an era where the Internet serves as a giant publishing vehicle," he says. "So anybody who has access to information, material or a script can immediately get it out there to millions of people. It becomes a big lure to see if you can spoil someone's fun."
     As a result, Carter has resorted to a technique sometimes used by big movie studios, stamping serial numbers on each page of every script so that leaks can be traced back to a specific reader.
     "I've also sent propaganda out to confuse and baffle," Carter said. "Fake information and fake story lines - things that we'd float in order to create conflicting reports and facts so that people wouldn't know what to believe."
     "Harsh Realm", adapted from an obscure, black-and-white comic book of the same name, is about a private eye who searches for a missing teenager in a virtual reality world.
     Only a few copies of the new "Realm" pilot-episode script exist, Carter said. And those that are circulating right now are printed on special red paper which makes it very difficult to photocopy.
     "It's impossible to keep scripts secret," moans one studio source. "because they're always sent out to agents to get the big-time [stars] to take parts in the shows."
     "I decided not to allow 'Realm' to go out to the agencies," Carter said. "I let agents come in and read it and I would send it to select actors with their name on it asking them to Fedex it back to us."
     When Jimmy Smits character on "NYPD Blue" was dying earlier this season, producer Steven Bochco shot Smits' final scenes on a closed set. "The guest stars only got the pages that they need to see," a spokeswoman for the show said.
     "Melrose Place," which is going off the air at the end of the year, delivered script outlines to top-level execs by hand in envelopes sealed with a wax and stamped.
     Inside were orders to destroy the script after it had been read. "It was like 'Mission Impossible'" a "Melrose" source said.