In the long tradition of the bedroom farce, from The Tales of the Decameron to TV sitcoms, adultery is oftern portrayed as seemingly the most fun a person can have without laughing. It's the kind of sport that never gets anyone down for long, and the adulterers, like those "weeble" dolls, always seem to rebound, heads-up and smiling.

But as most adults know, bedroom burlesque is to adultery what slapstick is to real injury. Actually, the theater of illicit romance is closer to cruelty than it is to comedy. There comes a moment on stage, after the dramatis personae have been slugging away at each other, when they discover that it isn't ketchup streaming from one actor's head -- it's the real thing.

Adultery is illusion and folly, headache, heartache and misadventure. Didn't Aristotle warn us that the affairs of man generally turn out badly? Will we never learn?

Apparently not. Despite every known warning, hazard and penalty, adultery does not seem to lose ist timeless appeal. Life offers too many occasions for this old biblical sin, rationalized by anger, disappointment, boredom or who-knows-what other outcome of matrimony.

At the heart of certain adulterous affairs is plain old malice, the kind inherent in James Thurber's admission that life offers no better feeling than to be in bed on a rainy afternoon with another man's wife.

Sometimes, adultery is an optimistic act: an attempt at diversion, a search for real romance or a little scherzo between the slow, dragging movements of domestic life. Some sourpusses like Oscar Wilde would have argued that adultery is necessary to maintain a marriage. (It was Wilde who said, "The happiness of a married man depends on the people he has not married.")

Whatever the causes and effects, anyone with more wits than a weeble knows adultery is rarely as funny as those picaresque tales of bed-hopping monks and maidens, or as delightful as the life-long friendship in the play "Same Time Next Year," or as essential to a man's well-being as the Ming Dynasty novels would have us believe. Yet there is never a shortage of people who will pay the price of infidelity.

It is to them that the following rules are addressed -- as guidance, caution and commiseration.

The names have been changed to protect the guilty.

Two half-loaves are worse than one, or: Why your love life is not better when it's complicated.

"I'd been living wiith someone for 10 years," says Rita, a comely woman in her 30s, "when we started to break up. Things had to end -- we both knew it -- but I felt I'd have to imprint with someone else before that could happen. The old relationship was like perforations on a page, but some tear was required to pull the holes apart.

"So I began an affair with this fellow we both knew. What I wanted was dalliance, not permanence. But I was so out of touch with that kind of thing that afterward I wanted to write a thank-you note to this person who out of the goodness of his heart had condescended to have an affair with me.

"It got to be terribly complicated. Two imperfect affairs instead of one. And since in this case two halves didn't make a whole, I was constantly worrying about both. Though I wasn't married, I still felt nervous about being seen and so on. It was so strange. The danger fanned the lust; but oddly enough, when we did go to bed, I discovered that wasn't enough.

"One of the worst things was waiting for him to call and then having to sit there while the man I was still living with hung on the telephone, making his own calls. It gave me the jitters and jingles to know at that very moment, in some phone booth, a man was trying to dial my number..."

Some one-night stands are memorable for the wrong reasons or: How innocent bystanders can get hurt, too.

Richard, a divorced father of two grown children, tells this story: "I once met a very attractive red-haired woman in a bar. It's not the sort of thing that happens to me often, but she ended up taking me home. She lived in Maryland, out in the country somewhere.

"When we got to her house, she did a weird thing. She went into a bedroom where her two small kids were sleeping and woke one of them up, talked to him a little and put him back to bed. She'd had quite a bit to drink, and I was still puzzled. Later on, I asked her why she would want to wake up a sleeping child. She gave me some sort of vague answer, something about wanting to make sure he was all right.

"I figured out that what was happening was this busines of parading the lover before the childen, even though they are not supposed to know. She'd been divorced for a couple of years, so maybe she wanted to show her kiddies she was still attractive.

"Anyway, the next morning, there we are in bed, when the door opens and one of the kids is standing there. At that point, the mother jumps up, tells me to hide in the bathroom, pulls the kid out of the room and slams the door shut behind her. I hear the conversation, which goes something like this:

Who is that man, Mommy?'

What man? There wasn't any man there.'

But I saw him ...'

You didn't see anyone, and don't you forget it.'

"I've often wondered how that kid turned out," says Richard.

The purpose of lve letters is to declare yourelf to your lover, but they also may serve to get rid of your spouse, or: How to admit that you are cheating.

When a lawyer warns you about the danger of putting anything incriminating on paper, he is ignoring what oftern turns out to be the purpose of a clandestine correspondence -- revealing the betrayal to the betrayed. For this reason, very few people are apt to be as circumspect as the character in the John O'Hara story who "began to receive some of his mail at the club."

A woman I know, who could think of no easy wat to bring her dull marriage to an end, hit on an ingenious (though, she swears, unconscious) solution. She began a long-distance affair that involved endless missives requiring many rough drafts. When the wastebasket in her study overflowed with the ball-up billet-doux, her husband's curiosity was sufficiently piqued. He, of course, stooped to read.

It worked.

Now she is wondering how to end her dull long-distance affair.

If you want to live a secret life, learn to live with secrecy, or: How to avoid runing a perfectly good marriage.

Steve, a comfortably married, middle-aged man, recounts the time when, as a young man who had been married only a few years, he fell hopelessly in love with a flighty young thing (had he but known it then).

One weekend, at the apex of his misery, he went to visit an uncle who had always been something of a father-confessor to him. After listening to his lovesick nephew examine his anguished conscience for hours, the uncle finally had this wisdon to offer: "You know, sometimes, when you've been living with another person, sharing everything, you get into the habit of telling that person everything you do, everything that comes along and happens to you. Uh, don't tell that other person."

Steve, who took this advice and is still married, says, "My uncle was referring to a very natural human thing. I can see there would be examples of disclosures made to a betrayed husband or wife out of other motives. You could be doing it out of cruelty, or to get absolution, or permission, or who knows what.

"But there is that other reality of having a strong impulse to pass on any kind of extraordinary information to the person you see every day of your life -- anything to break that deadly silence after 15 or 20 years of marriage.

"But that impulse should be immediately throttled -- unless you believe in the fatuity of letting it all hang out, and all the other cliches of sharing' and openness.'

"The moral, if you're going to cheat but want to stay married, is: Don't let it all hang out -- it's disgusting.'"

Romance and marriage can mix, or: Why a lot of bad affairs can keep a marriage togehter.

"But I know there's such a thing," said a young mman to a much older mentor as the two strolled through the Boston Common one day. "There has to be. I've seen old couples sitting on a park bench, holding hands, being affectionate, and I know it's love. And after all that time!

"You're right," said the older man. "There is such a thing. Why, I can see it just by looking at one my best friends, a fellow named Charly. Charly's a very successful, well-respected lawyer who has a wonderful life with a very nice, attrative wife whom he's been married to forever. They seem to really care for each other.

"The thing is that for most of their married life, Charly has fallen in love with other women with some frequency. Fortunately, it has always been with wildly inappropriate types: one, for example, was a practicing prostitute. It never works ouut, and meanwhile his marriage grows longer -- and stronger.

"I hapen to know this funny thing about Charly. A very nice thing, really. Every New Year's Eve, no matter where he is, or how drunk he may be, he'll go to the nearest pay phone with a bunch of coins and call up every one of his old girlfriends -- just to wish them Happy New Year."