You've gotten one or several. Or you know somebody who has. Or you're getting them now and living in fear, dreading the next time the phone rings. You're getting obscene, threatening, abusive or prank telephone calls. Like burglary or rape (and obscene calls are the verbal equivalent), the unseen caller spewing filth into the phone violates us, leaving us feeling helpless, afraid and angry. And though it may surprise you, obscene and abusive calls are a major problem in the Washington area.

The C&P Telephone Co.'s Annoying Calls Bureau (ACB) logs more than 20,000 complaints annually. That's just the complaints its staff of nine actually resolves, not all the unreported incidents or the sporadic calls the ACB can't track down. And complaints are up this year; 24,000 are projected for 1987. The ACB doesn't know why, but the number of complaints swells periodically -- when there's a full moon, for instance. "It's like the bottom's fallen out and everything's crazy," says an ACB staffer.

Yes, they can trace calls with what they call a "trap," but it's not the magically fast process you see on cop shows. When you call C&P's business office -- and you should, says the phone company, if you're getting four or more abusive calls a week -- the ACB will ask for the times and dates you received the calls so it can set the trap. The ACB doesn't tap your line and hear the caller. It can only produce the number where the call originated. Even with that, getting a conviction is hard because it's not easy to prove who's actually making the calls. As an ACB staffer says, ominously, "They know how to make these calls and get away with it."

Other than calling C&P, there are some things you should and shouldn't do if you become the victim of a phone creep. (I'll use "he" and "him" for clarity, but the ACB says everybody gets into this nasty act: Annoying and abusive callers are males and females, adults and children.)

HANG UP IMMEDIATELY. Both the police and the ACB say this is the first thing to do. In most cases the caller is trying to provoke a response from you. Don't give him what he wants by reasoning, pleading or threatening. Most important, don't attempt to trick an obscene caller, suggesting a meeting to which you can also invite the police. Even if your local constabulary would agree to participate in such a scheme (which is unlikely), the ruse smacks of entrapment, making a conviction difficult.

DON'T BLOW A WHISTLE INTO THE PHONE. Making a loud noise in a closed room is going to hurt your ears more than the caller's. (The phone line automatically dampens the decibel level reaching the caller, but you'll get the full effect of the blast.) And it challenges your adversary to call back and try to assault your ear.

CHANGE YOUR TELEPHONE NUMBER. This is an option, but with no guarantee of success. The sad fact, says the ACB, is that most abusive or obscene calls aren't made at random. They're coming from someone who knows you -- or at least where you live. And very often the caller will be someone you know by sight: a family friend, someone at work or your spouse's co-worker, a store employe or someone who lives in your apartment building. Yes, it's scary. C&P will change your phone number for free if you're being subjected to a pattern of annoying calls. But unless you get an unlisted number and keep it a very big secret, whoever's lurking out there may eventually begin the awful process again.

USE AN ANSWERING MACHINE. The ACB says this is a good method for handling certain kinds of obscene calls. If you're a woman, for example, you can have a male friend or your spouse record the outgoing message. (Which should say "We're busy right now so no one can take your call at the moment," not "Nobody's home . . .," an invitation to burglars.) Hearing a male voice or contacting an answering machine discourages many but not all obscene calls. Some people will leave offensive messages on the tape, but at least you can press the fast-forward button and speed past them.

Answering machines are less help if you're being harassed by someone trying to be annoying. Callers can fill up your incoming message tape with music or noises -- a bummer if your machine is essential to your business. But many machines let you limit the length of an incoming message to 60 seconds, forcing the pest to make repeated calls. Eventually, you hope, he'll get bored and find a new hobby. If nothing else, an answering machine is an electronic barrier between you and (in this case) the demented outside world. It lets you screen callers, identifying them before you pick up the phone.

USE A VOICE GENDER CHANGER. You've heard devices like this used on news programs when the person being interviewed has his voice disguised to protect his identity. Now you can buy a similar unit "to prevent repeated calls from unidentified or unwanted telephone callers." The quote comes from the Hammacher Schlemmer catalogue (1-800-543-3366), the only source at present for the DVC 1000, a Digital Voice Changer.

Speak into it (the voice changer is portable and attaches to any standard phone mouthpiece) and the integrated circuit digitizes the sound waves, breaking them into separate signals that can be reshaped by turning a dial on the device. By changing the frequency of the signals, you can alter the pitch of your voice, lowering it -- if you're a woman -- so it sounds like a man's. The gadget doesn't work quite as well in the reverse, however, and male users report producing weird computer-like voices when they've tried to raise the pitch of their own. But then, maybe sounding like a weirdo will discourage some weird callers.

The DVC 1000 also comes with a built-in pre-programmed synthesized barking dog. Switch on this digital canine and, by controlling the pitch, you can produce a terrier's yap or a St. Bernard's basso. But I'm not convinced the mere sound of a silicon watchdog will deter a buggy caller the way a live, barking dog might scare a burglar casing your place. The ACB says abusive callers almost never visit or make physical contact with their victims. Perhaps the manufacturer should have used the digitized background voice of, say, Clint Eastwood mumbling something about tracing the call and dispatching a SWAT team.

Still, the ACB says such a device might be useful for a woman living alone, particularly if she's been bothered by obscene callers. Be warned, however, that the DVC 1000 is not a sure cure, and at $500, it is certainly not cheap. And it may complicate matters if you are a single woman with an active social life. Imagine trying to explain the device to a new beau: "Don't hang up if a man answers. That's me . . . I mean it's my gender changer." ::