From Harvard, of all unlikely places, but of course from someone just a visitor there, comes something useful. It is a tract for these troubled times. Its title is "Common Courtesy: In Which Miss Manners Solves the Problem that Baffled Mr. Jefferson."

Miss Manners (a.k.a. Judith Martin) writes a splendidly authoritarian (and, in the bargain, authoritative) column for readers who like the smack of firm government. Although she reigns in Washington, she does not write about government as that is narrowly understood here. But Harvard's Kennedy School of Government, having sensibly despaired of perfecting the Republic with laws, invited Miss Manners to lecture on the role of manners. Her lecture supplies what the Founding Fathers forgot, "a philosophically acceptable and aesthetically pleasing standard of American etiquette."

The problem (my opinion, not Miss Manners') began in early July, 1776, when Jefferson was asked to go upstairs and draft a declaration of insubordination. He had a journalist's weakness for a snappy lead, so he began with that stuff about everyone being equal. Predictably, American etiquette suffered vertigo, and 200 years later a philosopher (Peter De Vries, who also writes novels) says that the trouble with treating people as equals is that they are apt to start doing the same thing to you.

The problem Jefferson left was: How do you express such American values as equality, individual liberty, social mobility and the dignity of labor in etiquette? As Miss Manners says, "The abolition of ancien-regime etiquette by French revolutionaries was all very well, but who wants to watch a bunch of revolutionaries eat dinner?" America's revolution was almost a black-tie affair, having been launched, in large measure, by landed gentry. But it has been laxly translated into an etiquette whereby you are assaulted in restaurants by: "Hi! I'm Donald and I'm your waiter!"

Donald is a practitioner of a common vice, instant intimacy through the universal use of first names: "All men are created . . . familiar." Donald may be of impeccable personal virtue and so perhaps should not be horsewhipped. But if he is not checked, the result will be, as Miss Manners says, "social chaos and the end of civilization, or about what we have now."

Miss Manners' target is the Jean Jacques Rousseau School of Etiquette, which involves the belief that natural behavior is necessarily beautiful and that rules only impede the spontaneous flowing of such beauty. She notes that the idea that Nature is benign is especially popular in earthquake-and flood-ridden California.

She also notes that we live in an age in which it is easy to insult people inadvertently. Ask any gentleman who has opened a door for a woman who is so bellicosely emancipated that door-opening is an affront.

And it is hard to insult people intentionally. Ours is an age of nonculpability; pop psychology has washed away personal responsibility with a blanket amnesty. If you say to someone, "You are disgusting and your necktie is vulgar," the person is apt to reply, with dreadful tolerance, that you are just feeling hostile because you are depressed and you will feel better tomorrow.

Miss Manners knows that a harmonious society depends on not treating all impulses as equally worthy of expression. It depends on reticence and decorousness, just as a durable marriage depends on the ability to say, with a straight face, "Why, I don't know what you're worrying about. I thought you were very funny last night, and I'm sure everybody else did too."

Miss Manners' theme -- that armageddon, not affection, is produced by substituting "honest self-expression" for the artifice of manners -- has an application to diplomacy. The American weakness for the Rousseau Etiquette translates into the belief that "frank" and "honest" dialogue between nations is bound to increase understanding, and understanding is synonymous with comity. Hence, the American enthusiasm, not to say giddiness, about summits. Hence, also, the unslayable faith in the Middle East "peace process." (The word "process" is popular with people who have an ideological or vocational interest in something sterile. Hence: "the arms-control process.")

Miss Manners recalls being president of a school board and differing with another member on every question. That member suggested taking the board on a retreat so they all could get to know one another better. Miss Manners said to him:

"You don't understand. The only reason I haven't murdered you is that I really don't know you all that well, so I feel I have to give you the benefit of the doubt. Do you want to remove that doubt?"

Ronald Reagan and Mikhail Gorbachev are going to Geneva to get to know one another. Thanks to Miss Manners, they, and you, have been warned.