Nothing more surely brings down the wrath of Post readers than the appearance of an earthy four-letter word in the newspaper.

It happens very rarely and, when it does, by policy either the word has the approval of one of the paper's top editors -- who will allow publication only if the word is essential to the story -- or it has escaped a reporter's care and an editor's eye.

Usually the ribald word is represented by dots or dashes, perhaps preceded by an initial consonant or vowel. This week, for example, NBC apologized for a single four-letter noun that came out of a program last week. The incident was reported in The Post, and the offending word appeared as four dashes, letters deleted.

These deletions are both part of newspaper tradition and a direct reflection of reader tolerances. Sometimes, writing technique is not enough. A few weeks back, The Post carried a paragraph that was heavy with meaning and replete with consonants and dots. Readers protested, and a newsroom staffer questioned in anger whether the paper's editors have young children at home who read.

In a different attempt to handle the problem. The Akron Beacon Journal recently published Jean Harris' well-known Scarsdale letter. The paper inserted a boldface paragraph between headline and story. The Paragraph read, "Some readers may find portions of this story objectionable."

There is a code at work in this lanaguage process.It has to do with a powerful cultural sense of what is appropriate. The code establishes severe limites, even though, according to linguists, acceptable language broke through several barriers in the '60s. Since that tumultuous decade, street and locker room words have invaded living rooms and dining rooms and social gatherings. Women feel more free to use what so recently was a bawdy noun or verb. If there is restraint in modern books, it doesn't show in the corner bookstore. Many movies, including Academy Award nominee "Raging Bull," move along on language that a few years back would have given graffiti a bad name.

These changes of usage have taken place in a language that, with the largest vocabulary among contemporary tongues, is relatively poor in obscenities. No student of lurid language will hold that English can contend in world-class sound-offs. There are timid championship claims for French, German and Italian; and not even that for Chinease and Japanese, to whose words, I am told, one must listen closely to recognize whether swearing is going on at all. It is said that Arabic curses can paralyze, that in Turkish one can sour good wine or wilt leaves on young tees in answer to serious insults and that in Hungarian and Romanian one can melt approaching bullets with words. There is a legendary Russian swearing competition that allows no repetition of language but may run on for two-and-a-half hours. In English, it takes skill and imagination to come up with more than a couple of dozen honestly raw words.

Limited or not, in this country salty language is taboo in a shrinking number of places: some families, churches, classrooms -- but not school hallways, family newspapers, government materials, public speeches to mixed audiences and radio and television shows, although they are subject to both cultural and statutory constraint. Readers and listeners are extremely sensitive about their perception of the propriety. They seem to agree with a 1978 Supreme Court ruling on protested language in a radio show. The court concluded that inappropriate language "may be merely a right thing in the wrong place -- like a pig in a parlor instead of in the barnyard."