After Nora Slams the Dora Note: Tomorrow, a new Stephen Sondheim and Harold Prince musical will go into rehearsal in New York. Called "A Doll's Life," it will address the question of what happened to Nora, the heroine of Ibsen's "A Doll's House," after she walks out on her husband Torvald at the play's end. The play stars George Hearn, last seen in Washington as "Sweeney Todd," opera star Giorgio Tozzi and Betsy Joslyn as Nora . . . The production will play in Los Angeles starting in June prior to a September opening on Broadway . . . Who Was That Masked Man? Note: If you ask that question in London these days the answer would be "an actor in the National Theatre's production of 'The Orestia,' " which is this year's surprise hit. The play, done in the Greek manner in which the actors wear masks, opened to reviews of the noble failure kind, but the public has been pouring in anyway to sit through the five-hour performance. The company has been invited to perform at a drama festival in Epidauros, Greece, this June . . . Sir Peter Hall, who directed the play, is not finished with his use of masks. He is at work on a masked adaptation of George Orwell's "Animal Farm" for the National next year . . . Apt Title Note: Peter Weir, Australian director of "Gallipoli," has been on location in the Philippines shooting his new movie starring Sigourney Weaver. After receiving bomb threats and death threats from what reports described as a "far-right religious group," he and his company pulled up stakes and headed home to Australia to finish filming. The film's title? "The Year of Living Dangerously". .

TRADITIONALLY, a luncheon is a lunch that takes an eon. Perhaps that is why this particular form of entertainment fell into second-class status in recent decades. That, and the ugly necessity of working for a living, and perhaps also the way that people look at 6 o'clock who have had three wines at mid-day.

The luncheon party used to be something quite jolly, however, and Miss Manners is seeing signs of its becoming so again. She is not talking about restaurant lunches, whether they are knee-to-knee or the kind where the guests go home afterwards with the floral centerpieces, but the formal, or approximately so, lunch given by private individuals at home for purely social reasons.

By definition, this sort of luncheon must be given by and for people who can wander off in the middle of the day from their jobs, and whose work will not suffer from any lapses of attention should they happen to wander back afterwards. That is why, when gainful employment became a universally desirable hobby, luncheons first evolved into "ladies' luncheons" and then virtually disappeared. Luncheons can be given on weekends, of course, but the guests will then treat them as brunches, wearing sports clothes and demanding Bloody Marys.

They are now coming back, because dinner parties have become so difficult. Hardly anyone knows a dozen people who will agree to maintain themselves in the same coupled or single state when the party occurs as they were in at the time the invitation was issued. And cooking has become so competitive that everyone who isn't terrified to offer a meal to self-designated "gourmets" turns the occasion into a demonstration and discussion of food, which is not what a social meal is supposed to be.

Luncheon is so much more accommodating. At lunchtime, you can invite the people you want, without having to have the people they want.

The food is simpler, three light courses being considered sufficient, and egg and salad dishes being quite respectable as main course. Anyway, everyone gets to fill up on bread and butter, which, you know--don't you?--do not appear together at formal dinner parties.

Damask tablecloths and flag-sized napkins are not needed. Even the most formal luncheons are served on place mats with square napkins. There are no candles to dribble on your bare table.

The custom of gentlemen wearing cutaways to Sunday luncheons and sack coats to Saturday ones having died out, formal dress, for a luncheon, is within anyone's reach (into their own closets). Hats are regrettably no longer required for ladies, but luncheons are an excellent opportunity to take them for a treat for those who happen to have them.

Best of all, people usually arrive on time for luncheons, and they eventually leave, which cannot always be said of the same people at dinner time. The reason is that they have the odd notion that one needs an excuse to depart from the scene of hospitality, and while "I guess I'd better be getting back to work" does in the daytime, they can't rack their brains for any reason for going home at night.

In short, the luncheon is a fine way to get around the modern difficulties that have made the dinner so difficult to give properly. What would be compromises at dinner are correct procedures at lunch. A formal luncheon solves all the problems one encounters at dinners, except one: the problem of what to say to your boss at 4:30.

MISS MANNERS RESPONDS

Q. I recently entertained a newly found acquaintance in my home. Afterwards, I noticed that some of my major credit cards were not where they ought to be--i.e., they were wandering the streets, rather than snug and safe in my wallet. I subsequently discovered my acquaintance had something to do with their disappearance. My question is, when I run across this person in the streets--and I am bound to do so as we are in the same social set--what do I say, if anything? You see that this is a rather delicate etiquette problem.

A. Miss Manners cannot tell, from your restrained recital of this distressing event, whether you are the sort of person who is tempted to smack the offender with your gloves, or the sort who wants to help him talk out his problem. Do neither. If ever there was an occasion for a cold snub, this is it. If the crime is provable--in which case why is this person still out on the streets?--it may be an obvious cut; if there is doubt, keep it a controlled snub that he alone will understand.

Q. Please settle an argument between my sister and me. I wore a navy blue dress and red jacket to a drop-in type wedding reception, 6 to 8 p.m., on Saturday evening (the bride and groom had been married privately a week prior). Another lady wore black. Very nice, but we were criticized severely, on the idea that one should not wear white, red or black to a wedding reception.

A. Critiquing the clothes of wedding guests is a wedding tradition, but it hardly seems fair here, as what you attended was not technically a wedding reception, which is held right after the wedding, but a reception in honor of a newly married couple. In any case, you were fine in red and blue. Before black came to be smart, as in the Little Black Dress, it was strictly the color of mourning, and therefore one did not appear in it at a wedding to spread one's gloom. White is considered competitive to the bride, who has the right to be easily spotted as the main attraction.

Q. My wife and I shall be moving into our first house in about two weeks' time. We intend to have an open-house party as a housewarming after we get ourselves settled and the house arranged to our satisfaction. We plan to invite all our friends, co-workers and the people at the church we attend. We had planned to include all the neighbors, but I recently read that when newcomers enter a neighborhood, it is up to the established residents to issue the first invitation. But since we plan to have the party relatively soon after moving in, we would not be likely to receive very much such, and so if we followed this rule to the letter, we may be faced with inviting some and not others, or none of our new neighbors. Might they feel snubbed if this happens? We want to be right, and we want to get off to a good start in the neighborhood. What do you recommend?

A. This must be Miss Manners' day for being an old poop. (Everyone should have such a day now and then, as it clears the air for unrelieved good cheer the rest of the time.) But she cannot see inviting totally unknown people to a party, no matter how warm your house and your intentions.

There may be, among them, someone in fresh mourning. Another may have been arguing that your coming wouild ruin the neighborhood. All of them will arrive in the crowd you describe, knowing no one. Some will probably discover their hosts by the look on your faces when they remark sociably how much tackier the house looks now than under the previous owner.

Appearances to the contrary, Miss Manners does not mean to discourage you from initiating friendly relations with the neighbors without insisting on their approaching you first. (Discourage? you ask. It hardly seems worth living now, let alone throwing parties.) She just asks you to do it individually, rather than throwing them in, unknown and unattended, with your already established circle.