In its library The New Yorker provides its writers with a characteristically handsome service: a running anthology, in black binders, of each one's contributions to the magazine. E. J. (for Ely Jacques) Kahn Jr., can muster the largest anthology of them all. A staff writer with the magazine for more than 40 years, he has paused, en route to depositing his 3 millionth word there, to produce this journal. Unlike nearly everything else he has written, none of its contents first appeared in The New Yorker.

Like many another New Yorker staff writer, Kahn, by his own admission, has no subject-matter expertise. His modus operandi is to concoct a topic that interests him, secure editor William Shawn's go-ahead, and write about it wittily, nimbly and well. There is no telling what he will scintillate on next.

Kahn's journal entries alternate between inside New Yorker anecdotes and autobiographical vignettes. Few of the latter are more than midly interesting. Kahn does know how to live the high life, whose essence, I take it, is dining, drinking, and quipping with the brilliant and rich; and he has engaged in one or more of these activities with Frank Lioyd Wright, Ogden Nash, Dorothy Parker, John Cheever, Walter Cronkite and david Rockefelle. But most of the autobiographical side of the book centers on Kahn's domestic life, which features two house and a confusing array of sons and stepsons. Perhaps because he lacks passionate commitment to any subject, Kahn in private is not a fascinating or profound fellow.

When he turns to the great magazine, though, he can be quite entertaining. Early in the journal he fires the first of several salvos at Brendam Gill's "Here at The New Yorker," published a few years ago to mark the magazine's 50th anniversary. Paging through "The John McPhee Reader," Kahn muses: "McPhee is, in my envious view, the best nonfiction writer The New Yorker has. It was characteristic of the frailty of the supposedly nonfictional account of the magazine and its contributors written not long ago by Bredan Gill. . .that John is nowhere mentioned in the book."

Kahn the tidbitmonger gives us such glimpses into the Magazine's inner workings as these. No one at The New Yorker knows why John Cheevr doesn't write stories for it any more. There is no secret to selling one's writing to the magazine. ". . .[Everything] sent in there gets read, and . . . without the discovery of new talent through unsolicited contributions from outsiders the magazine probably wouldn't have lasted . . ." Editor Shawn is a quasi-mythical figure even for those, like Kahn, who know him well: "I dream about Shawn more than I do about women," Kahn writes. And even after 40-plus years on the staff, Kahn is unsure-and agonizes over-whether Shawn will accept even an assigned piece until he actually gives the word.

Yet there are advantages to having been around the magazine as long as Kahn has. Once, a few years ago, Kahn had run out of article ideas, and Shawn knew it. "We chanced to meet in a editorial corridor one afternoon, he walking in on edirection, I in the other. As we drew abreast. Shawn said, without breaking stride, "Coca-Cola?' and I, also with out halting said 'Yes.' That one-second exchange was the only discussion we had of the project until I turned in my manuscript several months later."

Unfortunately, however, Kahn does not purvey the two potentially most interesting tidbits: the rates The New Yorker pays its writers and the extent to which its editors change his work. (All he says about editing is that they do it to him less than they used to.) Nor is he informative about the magazine's future.

Shawn is in his 70s, and an undeclared war of The New Yorker succession is quietly in progress. No matter who takes over, the magazine is sure to change. Indeed, under Shawn himself, who succeeded the legendary Harold Ross in 1951, it has grown weightier, more issue - oriented, more enamored of contributors, like Barry Commoner and the late Hannah Arendt, who excel at thinking rather more than writing. And as the magazine has become more solemn, its opening pages - the sketches, parodies, stories, and those cunning cartoons - have assumed the mind - quickening function of an ebullient over-ture before a somber symphony.

Kahn regrets this de - emphasis of wit and finds the younger staff writers a stodgy bunch. Yet event the magazine's long - standing ad campaign flaunts its increasing seriousness. A typical ad will quote teasingly from a trenchant article - say, Thomas Whiteside on the latest toxic chemical - admit that there is much more to it in the current issue, and conclude with the refrain, "Yes, The New Yorker." E.J. Kahn is an unabashed holdover from The New Yorker before it got its Yes.