AMERICANS CALL Alan Ayckbourn "The English Neil Simon" and the English call Simon "The American Ayckbourn," but it's not that simple.

Ayckbourn is the author of two comedies opening this week, "Absent Friends" at the Eisenbower and "Absurd Person Singular" at Olney. "Absurd" made its American bow at the Kennedy Center three summers ago and before that the Kreeger introduced his "Relatively Speaking." American's first Ayckbourn was "How the Other Half Loves," which Phil Silvers tried out at the National before going on to disaster in New York, where Ayckbourn's "The Norman Conquests" later deserved better than it got.

Above all, Ayckbourn is a dazzlingly ingenious craftsman. A former actor who now directs his own theater-in-the-round at the Scarborough (Yorkshire) Library Threater, Ayckbourn has written 14 plays in the past 10 years, using small casts and single sets, economies demanded by his limit of 254 seats. Unsubsidized, Scarborough has supplied a stream of financial winners for London's commercial West End. His latest, "Bedroom Farce," commissioned for the new National Theater, is in repertory in its Lyttleton Theater through the summer.

Like Simon, Ayckbourn breaks his pattern. In "Promises, Promises," adapted from Billy Wilders "The Apartment," Simon pulled off a musical hit. Ayckbourn adapted P.G. Wodehouse's "Jeeves" stories to a score by Andrew Lloyd Webber, who composed "Jesus Christ Superstar," but it mustered only 47 London performances. This spring, changing his style, Ayckbourn wrote about a good-natured man whose mother ruins his marriage in "Just Between Ourselves." Caught off guard, his usual public didn't dig it and the London run was brief. It was the sort of experiment one would have expected from London's National but it chose, instead, the more commercial "Bedroom Farce." Simon failed, too, with his rewrite of Job, "God's Favorite."

Balance is the most striking aspect of Ayckbourn's stagecraft. In "Absurd Person Singular" the settings are three different kitchens on three Christmas Eves. In "Absent Friends" three men and three women reunite on birthdays to help one of them forget someone. "The Norman Conquests" is three plays about the same six people the same weekend, but they have different settings: "Table Manners" in the dining room, "Living Together" in the "lounge" and "Round and Round the Garden" outside. "How the Other Half Loves," which Robert Morley played for three years, was another three-couple farce in which what at first seemed one sitting room actually turned out to be two different rooms.

AYckbourn admits "I like three. It's a comic number."

Speaking of the three bedrooms of three separate houses that are the setting for "Bedroom Farce," he observed that "running gags often pay off in threes. A baby usually will gurgle back at you after the third boo round the corner of his pram. If it's a baby with a sense of humor. Three is a symmetrical number. Yet it's unbalanced. Most of my plays are about people caught off balance. Besides, I couldn't get any more beds on the Scarborough stage."

Where Ayckbourn differs profoundly from Simon is in class distinctions. The best of Simon can be zeroed in on New York's upper West Side. America's upwardly mobile tradition has led Simon to plaza suiters and California suites but the characters are recognizably the same.

English class distinctions are very much a part of Ayckbourn's British acceptance. In "Absurd Person Singular" upper, middle and low-class couples get together in different, revealing kitchens but the aristocrats are on their way down, the middle duo is muddling through and the lower-class couple is aggressively on the rise. "How the Other Half Loves" got some of its humor from the mad setting of two disparate living rooms jumbled together as one, with the characters carefully sticking to the class-indicative furniture of each sequence.

"Relatively Speaking" is rooted entirely on Upper-Middle manners that forbid prying curiosity about the personal background of strangers, which is the first thing American strangers openly settle. All three of "The Norman Conquests" are predicated on the behavior of Norman, whose liaisons with three women of the same family break the rules. As Norman's wife puts it, "He claims that women can be divided into two groups, the ones you stroke and the ones you swipe. There has been some research done on this and it's been discovered quite recently that they are actually a little more complex . . . I always feel with Norman that I have him on loan from somewhere."

So accepted a part of English social tradition that they are unthinkingly accepted in Britains, these class distinctions are a barrier for American actors and audiences. As Shaw illustrated in "Pygmalion" and Osborne in "Look Back in Anger," there is no such thing as a British accent. There are several and all convey specific meanings.

Nor, for audiences' convenience, can Ayckbourn be transplanted to American, which was attempted with "How the Other Half Loves." Producer Peter Bridge, whose London production of it remains Ayckbourn's most successful, evolved an American setting for Phil Sivers rather against his own will, but with the disappearance of class distinctions much of its humor vanished.

One regrets getting into this sociology, for Ayckbourn shudders at being adopted by serious-minded theater pundits: "I'd hope not to have my plays included as part of the school syllabus and be loathed by a whole generation of schoolchildren. I write about real characters who, projected into incredible situations, start behaving in a larger-than-life manner as the situations appear to them too horribly real. I'm with Chekhov on this. He called his plays comedies or farces whenever he felt like it. Probably to confuse Stanislavski."