Martin, when one is bereft of a general system of etiquette. Well, these people have grown up and discover that it's not true, and they're at a terrible handicap.'' Job interviews, romances, all are in jeopardy, says Ms. Martin, are those children now in their late teens and early 20s who ''were told that etiquette is outdated and you just do whatever you feel like. Unfortunately, those who pay the price for believing such nonsense, says Ms. Martin, herself the mother of ''two perfect children'' - well, that's how the book jacket reads - politely snorts at the ''Jean-Jacques Rousseau school of etiquette,'' the belief that natural behavior is beautiful and that civilization, including manners, spoils man's essential goodness. the ideal revenge of a theoretically powerless person on a supposedly powerful one.'' Martin throws out some for the children who may be listening: ''Properly done, a sulk is wildly irritating to the parent.

However, lest anyone think the author is one-sided, Ms. Martin tosses in counsel that will warm parents' hearts everywhere: ''The chief tools of child-rearing are nagging and example.'' ''Lecturing, in Miss Manners's opinion, is one of the rewards of child-rearing.'' Interspersed with her advice on the etiquette of braces, car pools, and the like, Ms. Martin has modeled her second etiquette book on her column format: a brief commentary on a particular social breach followed by answers from ''Miss Manners'' to the ''Gentle Reader,'' one of 200 letters she receives weekly. In waging her genteel war on rudeness - which, by the way, does not permit ''being ruder back'' - Ms. ''Things were in a rock-bottom state when I first went into the etiquette trade six years ago,'' she says, sounding not unlike a modern Mary Poppins, ''but now there is a realization that you don't have to live in a world where everyone is rude.'' Just as she crisply stated her intent in her book: ''A good parent owes it to a child to teach manners as an interesting and useful skill, and not as a subject that is invoked to condemn whatever the child happens to be doing when the adult is feeling irritable,'' so does she mince no words in person.

Martin is no schmooze over the back fence. But that's what civilization is all about, and you have to start very young.'' ''It's very hard to teach a child to let somebody play with his toys or to wait.

Martin says, looking very proper during a recent interview in her high-necked blouse and antique garnet earrings. ''The baby doesn't think, 'Well I'm hungry, but if I wait a few hours they'll be less reluctant to get up,' '' Ms. Martin's strong suits, as is her no-nonsense advice. Judith Martin, offers her ''primer for everyone worried about the future of civilization.'' What this heir apparent to the etiquette doyennes Emily Post and Amy Vanderbilt proffers is highly practical but spirited counsel on modern-day manners and morals common to that process known as child-rearing. Or at least as we knew it prior to the '60s, a decade that, according to Miss Manners, was ''without rules.''ДЄs a tonic to the aforementioned plight, Miss Manners, who in real life is the syndicated columnist and novelist Ms. For this tome on decorum that is receiving all sorts of highly favorable book reviews has at its core nothing less than the ''passing on of civilization'' as we know it. Gentle Reader, as Miss Manners herself is wont to say, press on. Or commiting faux pas at parent-teacher conferences. Not for failing to use one's fish fork correctly - that was discussed previously - but for violating the rules of the baby-sitting co-op. One can almost feel one's metaphorical knuckles being rapped. My, my, Miss Manners is prolific isn't she? Barely has the dust settled from the rollicking entrance of the first etiquette epistle, ''Miss Manners' Guide to Excruciatingly Correct Behavior,'' than we are inundated by 389 pages of ''Miss Manners' Guide to Rearing Perfect Children.''

Judith martin gentle reader