A GUEST is someone who believes that a party invitation is an opportunity to be fed and watered in someone else's house, along with whomever he chooses to bring along, if he happens to feel like it at anytime after the hour specified. The idea that there is any obligation on his part, befor, during or after the party, would be a terrible imposition.

Why anyone should want to socialize with someone of this sort, much less open one's doors to such a boor, Miss Manners cannot imagine. And yet people continue to plan parties for the enjoyment of their friends -- and continue to be surprised and hurt that the warmth of their hospitable urges inspires no reciprocal urge to please in the friends they invite.

Miss Manners has noticed, in recent years, that no one believes that it is still a social custom to respond to party invitations -- no one, that is, except everyone who happens to be giving a party. The very people who wail at Miss Manners about what their guests' silence does to their plans, food bills and peace of mind do not conclude that they should answer the invitations they receive.

It is also considered an imposition to expect the guest to find sufficient company in the presence of the other guests the hosts have chosen. Guests figure that they must bring their own partners to amuse them, no matter how desperately they may have to work to round one up. (The exception is married couples who, being invited in pairs, tend to arrive singly.)

Guests consider it an infringement on their personal liberty to be expected to dress with any reference to the nature of the occasion as opposed to what they may feel like wearing at the moment. They don't mind complaining if the food and drink have been ordered without reference to their individual appetites of the moment.

Once there, they may choose to socialize with the guests they brought themselves, or with people who happen to be standing about, but would protest having to tolerate the society of anyone who does not happen to interest them. Some recognize the hosts' duties and avoid them entirely; others prefer to entice the hosts to ignore their duties altogether in their favor.

The time guests consider appropriate for departure is when they feel bored, however soon or late that might happen. And of course when that does happen, all connections with the event are at an end.

Miss Manners is sorry to spoil these people's fun, but the fact remains that guests are still obligated to respond to invitations; ask special permission to bring only those whom they cannot go out without (a house guest or the other half of a newly formed living arrangement); appear within the time limits set, dressed appropriately for the occasion; greet the hosts, however difficult it is to find them; appear to be satisfied with the food and drink; socialize enthusiastically with the other guests; and leave when the party is over, thanking the hosts.

For those who cannot manage all these social burdens, we have a great many establishments that allow people to set their own terms for entertainment. For the convenience of their guests, these places allow them to come and go when they wish and with whom, and to order exactly what they want. There are no obligations at all presented -- just bills. MISS MANNERS RESPONDS

Q. I am in my ninth month of pregnancy. I have been fortunate in that I have been able to maintain a state of excellent health and intend, therefore, to continue my professional activities as long as I am able.

This brings up the distinct possibility that I might go into labor at my office. While I have no intention of making a fuss, out of consideration for my coworkers (some of whom appear to be highly emotional with respect to my condition), should this situation arise, I would like to handle it with as much discretion as possible.

Are there rules of etiquette for going into labor while pursuing one's professional activities? If there are none, could you please suggest some appropriate guidelines.

A. There are rules of etiquette for everything, with the possible exception of whatever it was you did that got you into this state.

Offices are sometimes the scenes of unanticipated medical emergencies, such as heart attacks, and the rule for the patient is first to alert someone who can take charge of the situation, then to cooperate with legitimate assistance that is offered, and thirdly, if it is possible, to minimize the fuss, in order to avoid involving others who will only clutter up the scene.

As you can anticipate your need for help, you can arrange for it now. Enlist a trusted colleague to be on the alert to remove you from the office to the hospital quickly and discreetly when you announce that it is time.

The general rule to remember is that births are properly announced at the conclusion, not the onset, of the event.

Q. I work in a small office of 20 employees. Each year more employees are leaving Christmas cards on desks when the surprised recipient isn't there, rather than mailing them. This strikes me as an attempt to advertise their alleged poverty.

A. You are really overcome with the Christmas spirit, aren't you?

Hand-delivered letters are traditionally considered to be of higher status than those sent by mail, and the effect of 20 cents one way or the other does nothing to alter that.