The host or hostess who boldly states "Open House" on a holiday party invitation must face one of the inevitable consequences: Parents with toddling children will bring them.

Generally these are parents who are overly enthusiastic about each of life's endeavors, and bringing up baby is no exception. He is heir to all the latest manuals and methods, and among the current dictates therein is "Take the Baby Along." The parents feel a certain obligation to the child's socialization process, and anyway, where else -- if not a pary -- can the little tyke wear that red velvet suit grandma sent?

So, if you have as friends some of these enthusiastic types, expect Mama, Papa AND Baby Bear at your holiday gathering. To be somewhat steeled to this event, it is best to know what to expect. The following is offered as a precautionary outline:

Upon arrival, baby usually will be hesitant to enter a strange and noisy house. This will require one or both parents to remain outside in the bitter cold, cajoling the reluctant reveler.

When he finally does enter, the first of several temper tandrums will occur.

It will accompany snow-suit removal and introductions with the usual, "Oh how he's grown," etc., remarks drowned out by the volume of his screams.

After 10 minutes you can expect boredom to stop this initial performance. The toddler will then throw his energy clutch into high gear for other purposes. Investigations worthy of an F.B.I. team will ensue. The most attractive points of interest will be found on basement stairs and in kitchen cabinets.

NOTE: Clean vigorously the week beofre the party to avoid embarrassment, hair balls and dusty thread being among the favorite taste treat for an 18-monther. It also would be wise to leave the cat with your mother on party day and to hide your antique glass egg collection in the tank behind the toilet. Further, cancel plans for the flaming cherries jubilee.

Food, however, will momentarily distract most children. Naturally, most treats will be grabbed from a guest's plate, receive one taste, with the remaining portion dropped into the shag carpeting.

When baby's tummy reaches its capacity, be advised that he confines his spit-up targets to upholstered furniture or guests in dark suits. The same applies to any "leaks" he experiences.

If by chance the smallest guest receives a gift, he will of course find the ribbon and wrapping far more attractive than the present itself. He might display another annoying habit of children by breaking the gift during his first indifferent inspection. It will be left to the sputtering parents to gush thank you's and declare the fixative powers of a little glue at home.

There is a remote possibility baby will fall asleep during the festivities, but don't count on it. If this blessed event does take place, it will be of short duration and on someone's new rabbit jacket.

By leaving time, little Sunny Jim will have had a change of heart and find it equally as unagreeable to depart as it was to arrive. Above the noise of his cries and kicks, you must -- as it's your proper role as host -- assure both parents and child that it was indeed a pleasure to have them.

And the misty memory of the child's presence at your party will not fade quickly. Weeks into the New Year, after you've paid for the dry cleaning of the drapes and repaired the wicker chair, you'll be finding some of his toys in some unlikely places.

Mail them back -- fast.