UNTIL A FEW WEEKS ago, readers of the British satirical magazine Private Eye were regularly regaled by the diary of Auberon Waugh, son of Evelyn. This diary was conducted on the premise that Mr. Waugh was a bastion of the English squirearchy, a Tory in the 18th-century meaning of the word, surrounded by feudal vassals and possessed of political assumptions that made Mrs. Thatcher seem like a card-carrying Marxist-Leninist. From his supposedly castellated country seat, where (one was led to assume) unwanted visitors would be greeted by a cascade of boiling oil, Waugh penned observations upon the contemporary scene that were healthily unbridled by any regard for the niceties of fact or the law of libel. I wish I could quote a few lines to illustrate, but Waugh has not seen fit to preserve his ephemera in volume form, and the diary has, alas, now terminated with his removal to the editorship of a literary journal.

The real Waugh was, one gathered, rather a different character from the diarist: mild of visage, living in modest circumstances without a feudal vassal to his name, offering kindly hospitality to travelers rather than boiling oil. Such political feelings as he displayed in private were said to be tinged with at least a mild shade of pink. He was in other words a master-hand at the Spoof Diary: a genre in which a diarist only superficially resembling the real writer makes observations of a calculated outrageousness. Indeed, until I received my copy of The Papers of Samuel Marchbanks, I was under the impression that Waugh was the inventor and sole exponent of this genre. But, as I opened the Papers and dipped at random, it seemed to me that here was, at the very least, an affinity:

"Somebody told me a few days ago that they got the impression that I disliked children. Not at all: I love the little dears. But I have no patience with ill-mannered, noisy, destructive, rude, rampaging little yahoos and it is my misfortune, from time to time, to come in contact with herds of these, roaming wild in the streets; can anyone blame me if I drive them away with curses and blows?"

This is Marchbanks writing, but it might well be Waugh. And when I read in the introduction to the Papers that Marchbanks describes himself as "one of the last of a breed of Canadians whose racial strains and mental habits derive from those Loyalists who came north after the American Revolution of 1776," I was perfectly sure I had stumbled on a vital literary discovery: that Auberon Waugh's Diary was modeled on the "Samuel Marchbanks" column, which appeared from 1943 to 1953 in the Examiner newspaper of Peterborough, Ontario. Small matter that Waugh, in those days an English schoolboy, was not likely to be a regular reader of a newspaper published in Peterborough, Ontario. It is upon such hunches, however improbable, that great literary scholarship is built.

UNFORTUNATELY I have to record that random dipping (the tried and tested method of the reviewer) was in this case a strikingly inaccurate gauge of the real facts in the case. A reading of The Papers of Samuel Marchbanks from cover to cover reveals the following: (1) That "Samuel Marchbanks" (unlike Auberon Waugh) is a pseudonym. The real author of the diary is Robertson Davies, the distinguished Canadian man of letters. (2) That during the years in which the Marchbanks diary appeared in the Examiner, Davies was that paper's editor and owner. (3) That Davies subsequently published three volumes extracted from the Marchbanks column. (4) That The Papers of Samuel Marchbanks is an omnibus edition of these three volumes, consisting of 540 pages. (3) That Elisabeth Sifton, a distinguished New York editor and publisher, has issued this omnibus edition because she believes that Americans will be driven to uncontrollable spasms of mirth by Samuel Marchbanks. (6) That I am not of the same opinion as Ms. Sifton.

Marchbanks is certainly not without his charm, but it is the charm of a Pooter rather than a Waugh. Marchbanks' domestic trials -- such as his endless battle with his central-heating furnace -- occupy a substantial proportion of the chronicle, and inevitably recall the hero of The Diary of a Nobody trying to survive the rigors of domesticity rather than the asperities of a Waugh. Asperities, indeed, are not really in Marchbanks' line. They tend to peter out:

"To the bank this afternoon, and was once again amazed by the nonchalance with which the young women behind the bars treat my balance. To me it is matter of the most profound significance; to them it is a mere sum in addition and subtraction. Without being in the least aware of it, they can drive their cruel pens deep into my heart. That is, they are not aware of it unless I sink upon the floor with a despairing cry and attempt to disembowel myself with my pen-knife; then they call the assistant manager to throw me out. Banks hate suicides on the premises -- looks bad."

I fancy that Waugh, writing on the same topic, would have implied that he had several millions in his bank account (all in gold sovereigns) and that he had arrived at the bank by hansom cab, or maybe in a sedan chair carried by four crippled retainers. And without that element, something essential has gone. Marchbanks should lord it over his oppressors; instead, he cringes.

It is a pity, for he is far from devoid of humor. In one of the footnotes added to the omnibus volume, he (or his alter ego Davies) observes that the present-day computerized address machine "scorns anyone whose name contains more than twelve letters," and so has reduced him to "Samuel Marchb," who "sounds like the kind of Middle European poet who gets the Nobel Prize because the Russians (probably quite rightly) can't stand him." Indeed, I shall probably be deluged with abusive letters from the inhabitants of Peterborough, Ontario, assuring me that they have not stopped laughing since Marchbanks first set pen to diary in '43. But I do wish that the Marchbanks features wore a little less of the Pooter humility and had a touch more of the Waugh hauteur.

Humphrey Carpenter, biographer of J.R.R. Tolkien and W.H. Auden, has recently completed a life of Ezra Pound. CAPTION: Picture, Robertson Davies, (c) 1986 BY THOMAS VICTOR