MODERN MODESTY is difficult to define, even for Miss Manners, who does that sort of thing so well. Is it, for instance, immodest to wear a bathing suit on a nude beach, thus calling attention to one's body?

Worse than immodesty of dress or undress, in Miss Manners' opinion, is the current immodest fashion for dressing up one's experience so that one appears to be more than one really is.

The ideal of the well-bred person should be, as the German proverb has it, "To be more than you appear." This proverb predates the invention of the Mercedes-Benz, paid for on installments.

The concept of appearing to be less than one is survives now only in the tattered blue jeans worn by rich kids. Everyone else is busy trying to appear to be more sexy, rich, sophisticated or youthful than he or she really is.

Magazines and paperback books are full of suggestions to help one fool people about one's identity. The techniques are getting increasingly complicated. It used to be thought that if a newly divorced, middle-aged wage-earner merely bought a sports car and an oversized bed, wore a turquoise-and-silver necklace and shoes with hose bits on them, and, of course, unbuttoned his shirt to the waist, no one would ever know that he was not a 21-year-old rock star9

Now he is also told to purge himself of some dated popular culture, recast other such information as improperly learned pseudo-nostalgia, and memorize the current week's supply. He is warned to pay attention to such details as faking the contents of his kitchen cabinets in order to give an impression of being a fancier of good cooking.

The popularity of places where one's background is not checked, from discos to holiday "clubs," is not surprising when there is such a passion for falsifying.

Miss Manners questions whether image-inflating leads to happiness. She is not recommending the shocking policy of face-value honesty, but merely calling attention to the pleasures of being discovered to be better than one has presented oneself to be.

The cottage that turns out to be a palace, the "Mr." or "Ms." who turns out to have a doctorate, the gray-haired person whose face looks younger than that of an old blond of the same vintage, the struggling business person who turns out to be a tycoon -- it is when these discoveries are made that true joys of modesty are experienced.

But such things rarely happen in an age when people are constantly confessing to being discriminating and demanding connoisseurs of life. It is getting so that Miss Manners' heart skips a beat if her dinner partner declares that he knows nothing whatever about vintages of wine. MISS MANNERS RESPONDS

Q: Please, could you tell me what the duties are of a godmother, so named at a child's christening? I have been one for 35 years and have been chided about neglecting my responsibilities. Is it too late to do anything? What should I have done?

A: The responsibility of the godmother is to see to the spiritual upbringing of the child, so that the world is not full of adults who chide their elders about neglecting their duties.

The formal side of the job is to educate the child in the history, beliefs and ceremonies of his or her religion. The informal side is to provide the child with a concerned older person who is certified as responsible by the child's parents but has the advantage of not being a parent. Both of these services can be of great benefit to 35-year-olds, as well as children.

Q: I have been invited to a wedding next month, when I will be seven and a half months pregnant. I have a black maternity party dress -- is it proper to wear that?

A: Marriage, childbirgh -- there is a whole cycle of life behind this seemingly trivial question, isn't there? Miss Manners pictures you, in your charming dilemma. Having been a bride once yourself, you are sensitive to the dress violation of wearing black to a wedding, and thus lending a sort of bad witch appearance to an otherwise light event. At the same time, you have your child's future to consider. What sort of heritage will a child have whose mother squanders her money on a party dress she will only wear once?

Miss Manners' feeling is that while it is incorrect to wear black to a wedding, it is insane to invest good money in another party maternity dress. Use the plack as a background color, adding a light coat, shawl or scarf to disguise it, if not you.

Feeling incorrect? Address your etiquette questions (in black or blue-black ink on white writing paper) to Miss Manners, in care of The Washington Post.