Was President Reagan really surprised when scores of his friends poured out, shrieking Happy Birthday, or did years of acting produce that expression of stunned delight?

Is anyone ever really surprised, despite party preparations which can combine the coordination of an allied landing with the secrecy of the CIA? Maybe not, but the planning is fun and if the probability of success isn't very high, ther's always the chance that this time, this one will work.

There is the surprise shower -- wedding or baby -- where women, fearful of saying too much, begin to avoid the guest of honor, giving her a case of the nobody-loves-me blues. This sets her up for the party, where guests stuff themselves and their packages down behind chairs and couches and get ready to shout SURPRISE! A car pulls up with the guest of honor. Immediately, another car arrives and out jumps a late guest, carrying a gaily wrapped package.

Fizzle. A roomful of crouching, deflated people trying to untangle themselves from each other and the furniture.

Any successful surprise party needs Red Zone -- a half-hour or hour when late guests are told not to arrive. Come early or come late, but arrive in the Red Zone at your peril .

There is the husband who lures his wife to the surprise party by telling her they're going out for the evening and then, carried away with his ruse, invents a program of dining, dancing and champagne. But first they must make one brief stop and there, surprise, surprise, surprise, it's Bob and Joan and Carl and Alice and buckets of beer cooling in the refrigerator.

Don't make the cover story better than the surprise.

On the other hand, don't make it too much worse. One surprisee was invited to a friend's house for dinner, just the two of them: "I looked like a slob, I had on an awful, ugly jumpsuit, and when everyone yelled 'SURPRISE!' I almost turned around and walked out."

Sixteen chickens tucked away in the refrigerator and a case of wine cooling in the bathtub are a dead giveaway that this is not to dinner a deux, so don't even try to give a surprise party in your home. Attempts to maintain the surprise by sending your spouse on a futile errand or worse asking the boss to invent a work emergency, will result in a tired and grumpy surprise. And the worst surprise is that often as not no one helps to clean up.

Perhaps Nancy Reagan's plan was best, a bait and switch, where the person knows something is being celebrated, but not what. That way, when everyone shrieks SURPRISE! it's to a person who's wearing his dancing shoes.