THE NEW YORKER once had the official policy of calling its shorter articles "casuals." Or to slip into the style of those articles, it had the habit of calling them that. "Official" and "policy" are both large earnest words, and they wouldn't fit into the offhand manner of a casual at all.

The offhand manner, the trick of seeming never to take anything quite seriously, the appearance, even, of examining all things quizzically through a monocle -- the elegance, in short, of the casual -- that was one of the things that first gave The New Yorker its reputation. There are even people who think the magazine invented the form.

It didn't, of course. Under various names, the casual essay has been around for a very long time. It has been a particular specialty in England, used and loved by generations of elegant cool-voiced writers. One of the coolest and most elegant was the novelist Rose Macaulay, a member of the same family that a century earlier produced that very uncasual historian Lord Macaulay.

In 1925, shortly before The New Yorker was founded, Miss Macaulay published an enchanting book of essays called A Casual Commentary. There are about 40 essays in it (39, if you must know -- but it's breaking all the rules of casualness to have counted). Two generations later, most of them remain intensely pleasurable to read. Considering that Miss Macaulay wrote solely for an English audience, and considering that what she wrote was a series of offhand reflections on events and ideas of the early 1920s, with no thought for posterity or high art, and considering that the book is hence both parochial and ephemeral, this is no mean feat.

What keeps the book so readable, is, of course, the style. Imagine a Martian visitor writing articles about what she sees on earth. Imagine that Martian with a flawless command of English, a benevolent but wholly detached view of human beings, and no illusions whatsoever. Imagine her a mistress of dry wit. You have something like Rose Macaulay.

Take the several essays she devotes to politics. None of them are angry or accusatory or anything like that. They are merely cool and devastating.

For example, one of them tells people how to vote -- always a handy thing to know in an election year. The historical case is that at the moment she wrote, the Conservative, Liberal, and Labor parties were all vying for power in England. Each claimed, even as political parties do now, that the very welfare of the nation depended on its candidates getting into office. Miss Macaulay tended to the opposite view.

"Every now and then," she wrote, "there is a parliamentary election, and then every voter has to decide which of the various candidates who offerthemselves as representatives of his constituency he least dislikes, and considers least foolish and useless . . ."

Before the reader even has time to count the number of insults to politicians contained in that suave sentence, she has moved on. "Be sure they will all be quite useless, quite foolish, and quite unable to show any reason why they should represent you. This cannot be helped. Members of Parliament are like that, and that is partly why governments and constitutions are as we see them."

So what's a poor voter to do? Simple. If he or she is especially naive, go for the nearest Reagan-figure. Otherwise, pick the candidate who is best at painting rosy futures. Or as Miss Macaulay puts it, "Unless the voter prefers merely to vote for the candidate with the more amiable smile and pleasing address, he had better discover which of them will make the greater number of promises concerning the amelioration of the condition of the constituency. Judicious approach will be found to elicit a emarkable number of these promises from both sides. The promises will not, of course, be kept, but they are good things to have in writing, as they enable the members' constituents to make his parliamentary life a burden to him with reproachful letters."

IN ANOTHER essay she considers the question of what people would really like that politicians and governments can offer. She says (correctly, I think) that most of us are quite unclear.

"Vaguely we know that we do not want the politician, that we do want cheap things, no taxes, peace abroad and at home, plenty, a government which interferes with us as little as possible, and no fuss." How to arrange this? By withholding power from everyone, or at least from every public figure. The best thing, she says, would be "to have a House of Commons consisting of three minorities, so that none of them can do anything at all, since we have a well-founded belief that doing is a deadly thing, doing ends in death." She had World War I in mind; an American now can think of Central America, dead Marines in Lebanon, maybe even of the arms race.

But politics are the least of Miss Macaulay's interests. Literature pleased her more; and many of the essays offer advice to writers, to readers, even to journalists. I'm especially fond of an essay she devotes to the aspiring novelist. She has already explained that novels are absurdly easy to write, and that they have the great advantage over most kinds of books that a certain number of people actually read them. Now she is telling the young novelist what to expect after publication day.

"You need not mind what reviews say, for they are not much read except by you and your publishers. But you must make your publishers say, often and conspicuously . . . that your book exists and has sold many copies, for if the general public are told this loudly and often, they hasten to read it; they do not mind whether or not it is good, so long as they believe many others have read it. You must, therefore, make friends with your publisher and get him to proclaim you well. He should, for instance, in public announcements, always add a nought to the number of copies he has sold of your book, so that five hundred has the air of being five thousand, and so forth."

Excellent advice, that, made quaint only by the relative smallness of the numbers. Fortunately, many publishers now seem to be adding two noughts.

BUT NEITHER politics nor publishing was Rose Macaulay's central interest in A Casual Commentary. Women were. She was an early feminist, though obviously never a wild-eyed one, and many of the essays turn on the special concerns of women. Housekeeping, for example, and how to get rid of it. Miss Macaulay considers various ways to accomplish this desirable goal, including the currently popular one of turning it over to men. In the end, she has a more radical idea.

"The only solution to this problem which I can suggest -- and I hesitate to do it -- is, Do not keep house. Let the house, or flat, go unkept. Let it go to the devil, and see what happens when it has got there. At the worst, a house unkept cannot be so distressing as a life unlived."

Just for a moment our Martian was almost serious.

But she soon recovers. Even when there is real injustice to consider, her tone remains casual. It does, for example, in my favorite piece in the whole book: the double essay called "Woman: I. Her Troubled Past" and "Woman: II. Her Dark Future." (She actually considers the future of men as well. "I find it difficult to separate the probable destinies of the two creatures," she explains.)

If you have a taste for mannered writing, if you are one of those who see that keeping your emotional distance is one of the ways of turning tragedy into comedy and pain into pleasure, Rose Macaulay can hardly fail to delight you. Read A Casual Commentary, and then you might en want to try some of her 23 novels. Myself, I'd recommend The Towers of Trebizond. It's the last, best, and wittiest of them all -- the crown of a career as novelist that began in 1906 and didn't end until 1956. Note on availability: Except for an expensive reprint edition, designed for a captive audience of libraries, "A Casual Commentary" is out of print. Farrar, Straus and Giroux has a paperback of "The Towers of Trebizond" for $5.95, however -- and one can usually pick up second-hand copies of "A Casual Commentary" for $10 or less.