COMMITMENTS : Invitation to Disaster? : Few of us like surprises. Which is why even fewer of us like the idea of being surprised by a party.

“Guess what?” says the conspiratorial voice on the phone. “I’m throwing a surprise party for Joanne’s 40th. Her husband and I are doing it. We’re inviting ab-so-lute-ly everyone she knows. Don’t breathe a word!”

But the friend in question hates surprises. If anyone fussed over her birthday, she said last week, she’d shove their satin shoes in the clam dip.

So, do you call and warn her? Or just show up and wait, one of 50 furniture-crouching guests poised like an army of jacks-in-the-box, ready to pop up and yell Surprise! when she walks in, unsuspecting, underdressed, her teeth maybe under-brushed?

Not that this is the moral dilemma of the decade, or anything. It’s just a little party--right?

Well, sort of.

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In the annals of social interaction, there may be no quirkier mystery than what the birthday gods were up to when they created the surprise party, the deceptively simple ritual that unearths the unexpected.

The biggest surprise is finding out how well your nearest and dearest really know you.

At first, it seems like a perfect idea. Imagine: Clam dip just so, breathless guests waiting. Guest of honor walks in expecting to find one friend and a take-out pizza, but instead finds a This-Is-Your-Life love fest. The sheer joy of it! The tears. The hugs. The humble refrain, “I can’t believe you all did this--just for me!”

That party has happened about three times in history.

What happens those other times? We’ll tell you, but don’t breathe a word!

The Hold-Everything Scenario:

“The surprise party for my uncle’s 50th birthday was probably the worst experience of my life,” says a 36-year-old woman whose favorite uncle had lied for years about his age. “My husband and I drove down with a car full of trays of lasagna, champagne and a Carmen Miranda cake for 60.

“My uncle comes home from work--an hour early. He starts screaming, ‘What are you doing? I told you I didn’t want a party! How could you do this to me?’

“Forty-five minutes before the party, I had to call everyone and tell them not to come. We packed the Carmen Miranda cake and lasagna, drove to a friend’s house and ate lasagna. We had lasagna for months.”

That was eight years ago. The result: Uncle and niece love each other dearly, but still can’t talk about lasagna.

The Oops Scenario:

“My mother was having a surprise party at our house for my 16th birthday,” says a 22-year-old Arlington, Va., graduate student. “I was at a girlfriend’s house after school. She was supposed to stall me. At 4, I said, ‘I have to go home and study.’ She kept saying things like, ‘Why don’t we try this fabulous new dual-shade eye shadow and hair dye?’ I was like, ‘No, I really have to go.’

“Finally, she just looked at me and said, ‘You can’t go. We’re having a surprise party for you.’ I said, ‘Oops.’

“The awful part was trying to act surprised when we got there. I kept practicing in the mirror: ‘Oooh! I’m soooo surprised!’ I felt ridiculous. All I remember is thinking how crushed my mother would have been if she found out I knew.”

The result: She will never give a surprise party.

The Friendly Warning Scenario:

“A good friend called and said, ‘I feel morally obligated to tell you this: (A mutual friend) is planning a surprise birthday dinner for you,’ ” says a 44-year-old Minneapolis legal writer.

“It put all the worry on me, like who was or wasn’t invited, but not being able to do anything about it. In retrospect, I’m glad I knew instead of being blindsided. I walked into this fancy restaurant, trying to look wonderfully happy, but thinking, ‘I feel so horrible all these people had to spend all this money on overpriced lamb shanks.’ It was weird.”

That was six months ago. The result: “I still haven’t recovered.”

Surprise!

The trouble is not a particular cake, setting or guest list, surprise-party survivors say. It is, rather, what those details add up to.

It starts with the element of surprise itself, a thing nature abhors. It’s why Jolly Good Fellow has been known to walk into a room unawares, see a blur of faces, eat a few potato chips, and spend the whole evening feeling like a passenger on an aging commuter jet whose pilot is having a bad hair day.

“The recipient is completely out of control but may not know it,” says Judith Sills, a Philadelphia psychologist and author of several books on human interaction.

“People go through the world with a basic sense of what to expect. Being suddenly placed in an environment where what’s going on hasn’t been processed by the brain causes a sensory shift.”

Rule One: Make sure the recipient enjoys surprises.

“That person is really put on the spot. Everyone’s watching to see how they react,” says Cal State Fullerton psychologist Jinni Harrigan, a social-interaction expert. “If the person is depressed, going through a major transition or socially phobic, maybe it’s not such a good idea. You don’t want someone running out of the room screaming.”

Or even secretly wishing they weren’t there.

“If I had to do it over again, I would have liked to have known what I was getting into,” says a Bay Area grade-school teacher who had planned to spend her 50th birthday in quiet reflection.

Her husband and friends, “in a total act of love,” planned a surprise gathering of out-of-town family, new friends, old friends, childhood friends, parents of students, the works. She wore flimsy sandals, expecting to show up, say hello and leave a party for someone else.

She entered a concrete-floored museum. The sandal-concrete combo killed her surgery-weary feet. She had to slip in and out of personas from various stages of life. She managed to say something that truly offended one of the friends who’d planned the party. She was a wreck.

“I think I slipped into menopause and never recovered,” she says.

Rule Two: Think about why it needs to be a surprise in the first place.

The reason we give surprise parties, experts say, may be rooted in our own species-wide ambivalence about asking to be the center of attention. Somewhere, deep in that imperfect psyche, we feel undeserving; maybe even unable to name 20 people we think would give a royal hoot. Other people, we figure, must feel that way too.

“Giving a surprise party can allow someone who loves you to satisfy that piece of you that secretly wishes for it while that more boisterous part says, ‘Oh no, no, no, I hate parties, I don’t want one,’ ” says psychologist Sills. “It’s about me fulfilling that unspoken desire you may have.”

It’s simple: You say you don’t want a party, so I think you really do. Because when I say I don’t, I mean I do. So the party for you is really because . . . I want one.

Rule Three: Don’t forget whose party it is.

The event itself, through nobody’s malice, can grow into something far out of sync with the needs or desires of the person being honored. “It’s like the person gets lost in the shuffle,” says the honoree with the flimsy-sandaled feet.

And that’s when the real surprise sets in. Your honoree looks around the room at a crowd she wouldn’t have chosen and food she wouldn’t have served in a place she wouldn’t have gone to. She realizes, to her horror, that either her loved ones don’t know much about her, or, if they do, they’ve forgotten what it was.

Says Sills: “The issue is not, ‘I hate surprises,’ but rather, ‘What you’re doing is outside my comfort zone.’ ”

The secret to giving a surprise party that works? Says psychologist Harrigan: “You have to be truly sensitive to the person you’re honoring.”

But there’s a final hitch. If something does go wrong and the honoree ends up in a tailspin, the party-givers may not ever know. Nobody would breathe a word.

So it’s clear. The only honorable thing to do: Call to warn your friend about the impending surprise.

“Guess what?” you say.

“I know,” she confides. “Three people have told me. The party sounds wonderful. When it’s time to open the champagne, call me. I’ll be in--surprise!--Jamaica.”