ACCORDING TO THE old joke, a * New Yorker short story is the same as a Saturday Evening Post short story without a beginning or ending.

Now Penelope Gilliatt, the acerbic British movie critic for the New Yorker (a position she shares with the slightly less acerbic Pauline Kael), has taken the formula a step further; she has produced a "novel" by stringing together a series of just the sort of dry martini, upper-crust and stiff-upper-lip character sketches the New Yorker is famous for. And like a long bout with dry martinis, it may be fun, but ultimately there's very little nourishment in a handful of olives.

The Cutting Edge, Gilliatt's first novel in 12 years, is summarized in a tense paragraph in the publishers' promotion letter: "Two brothers as close as twins and the women who loves them both set the stage for... a witty, sophisticated story which examines our emotional links with others, our search for security, and the ageold problem of self-identity."

Peregrine and Benedick -- who for part of their childhoods are simply called "Brother A" and "Brother B" by their unhurried father, and who narrowly escaped being named Eustace and Osiris -- are, as advertised, doppelganger close: similar in appearance, sometimes telepathic, communicating as children in a private language which allows them to make improbably astute comments about the adult world. Although she may have originally intended to use each brother equally against the other, Gilliatt is plainly more interested in Peregrine, and as the book progresses, Benedick more and more provides a foil for his older brother. Benedick also is enlisted to speak some of the more preposterous lines by Gilliatt, who may have had a sneaking suspicion that her little archness was going too long a way.

Gilliatt says about Peregrine that "His life was like a psychological slip, disclosing the forbidden wishes that plough up an age." Benedick comes back with a memo to himself that "'Peregrine's life is moving, not in itself, but for having been undertaken, for it does seem undertaken, like a piece of work.'" Peregrine is alternately ludictors and endearing; Benedick careens between dumb doglike devotion to his brother and rare bursts of intelligent self-interest.

The language of the book is determinedly literary, and often extremely effective; but it is most effective when most succinct. There are quick, glittering sentences ("He began to live in a chill delirium of work") and passages of extraordinary humor, as when Peregrine, who speaks little Italian, attempts to explain to his housekeeper in Positano that he is writing a play in poetry about a homosexual and instead informs her that he is composing a tragedy about spinach.

Gilliatt is keen to follow through with her investigation of "emotional links," etc. She loads the brothers down with a mirror image -- another pair of siblings, these a set of twins, their illegitimate younger half-brothers. She then has Peregrine and Benedick change their hair and even their eye color (via contact lens) to more closely resemble one another. But three-quarters through the book having moved Benedick's ex-wife Joanna in with Peregrine, Gilliatt gives up. We know almost nothing about Joanna, little about why she left Benedick and even less about why she moves in with Peregrine. There is no ending and precious little ambiguous conclusion. When Peregrine says portentously, "I don't know whether you're in love with me because I'm like Benedick or because I'm not like Benedick," Joanna comes back with the one natural retort in the entire book -- she tells him to shut up.