London theater: a frothy comedy and a biting social commentary

British theater critics are generally irritated by anything commercially contrived - particularly when it is blatantly aimed at attracting American tourists.

This is the reason a production at the Theatre Royal Haymarket here - ''Aren't We all?'' - has been roundly panned. The frothy 1923 Frederick Lonsdale revival puts two vintage stars (Rex Harrison and Claudette Colbert) on the same billboard at the height of the late-summer, early-fall season - and offers large dollops of nostalgia - for no other reason than to draw the overseas visitors.

Lighter than a well-whipped meringue, the plot seems quaint at best, while the jokes smack of the kind of upper-class stereotype humor the British use today only for export.

Nonetheless, the show is packing them in, and there is the possibility it may be extended beyond its original late fall closing date. It's that much of a hit.

Harrison displays all the legendary ease and wit that have made him a master light comedian of the British and American stage. In fact, from the mouth of another actor with only slightly less polish, the lines would have surely fallen flat: thinly written, they need the subtlety of a raised eyebrow, a twitch of the leg, or a carefully timed hand placed in the pocket to make them work. Harrison, at 76, still clearly knows how to do it best.

As for Colbert, although no one would accuse her of ever having been a great stage actress, she has over the years lost none of her charisma. Harrison has only to exclaim upon her breezy entrance, ''You look younger every day'' - to which Colbert, a remarkable-looking 81, quips back, ''I'm glad of that; it takes me all day to do it!'' - and the audience burst into rapturous applause.

Author Lonsdale wrote pre-Noel Coward ''drawing-room comedies'' which, according to 1920s sensibilities, meant lots of mirth with little meaning. So we find a fast plot crafted for caricatures rather than characters. In it, the Honorable Willie Tatham is seen by his wife, back unexpectedly from a jaunt in Egypt, being lured into a kiss by a conniving vamp during a party in their Mayfair home. All quite innocent, really, the Honorable Mr. Willie insists.

But the Honorable Mrs. Willie doesn't buy it. Shaking his head at his son's ineptitude in handling being caught, Lord Grenham (Harrison) quickly takes over and tries to woo his daughter-in-law back to reason.

Meanwhile, Lady Frinton (Colbert), an American widow of a British knight, is a house guest trying to bag the elusive Lord Grenham for her own - ''I cannot deny a woman anything,'' the dapper old bachelor says dryly, ''except marriage.''

Lady Frinton's main function is to flit in and out as the cool, clever-tongued foil for Lord Grenham's drollery. Within this vein the play has more than a few good moments. The supporting cast is strong, the sets suitably lush - and when Lord Grenham is finally tricked into Lady Frinton's marriage trap, Harrison plays the scene with rare comic perfection.

This is one of Harrison's infrequent appearances on the London stage, while Colbert last performed in a theater here in 1928. They are well teamed.

Indeed, the evening seeks nothing more serious than to entertain. And so it does.

Weightier stuff

For more meaty theater fare, however, there's ''Benefactors,'' by Michael Frayn, which is surely destined for a long run nearby at the Vaudeville. It is, without question, the West End's best new work of the year.

But fans of Frayn's most recent hit comedy, ''Noises Off,'' may be a bit disappointed - this is not a hoot a minute. There's lots of humor, to be sure, but of a more biting kind.

This is a quiet, complex play which dissects do-goodery - as distinct from doing good - to reveal how it often masks utter indifference.

With a cast of only four, Frayn deftly makes this point on many levels. The quartet are neighboring couples somewhere in the suburbs of liberal middle-class London. David Kitzinger (Oliver Cotton) is an architect married to Jane (Patricia Hodge), a well-bred anthropologist who now devotes herself to raising three children and conducting housing surveys for a building preservation trust, while at the same time being both constant consoler and bottomless coffeepot for her helpless neighbor, Sheila (Brenda Blethyn).

Sheila, meanwhile, is married to the forever cynical Colin Molyneux (Tim Pigott-Smith), a failing journalist and former Cambridge crony of David's.

They are all self-absorbed people. The Kitzingers are the do-gooders - the benefactors - of the play, but they cannot see past their own noses to give of themselves in a way that will genuinely benefit those whom they are ostensibly helping. In fact, neither one really understands or, for that matter, cares much about his or her fellowman. David's ambition is to demolish a working-class part of London to build high-rise tower blocks. Jane, meantime, with all her surveying and neighborly sacrificing, finally admits: ''I don't think I like people very much.''

Colin and Sheila are the takers - the constant beneficiaries - of their neighbors' knee-jerk bonhomie. But it's a symbiotic relationship: In return, they give David and Jane endless fuel for conversation, while making the couple feel good about themselves.

Most of all, however, ''Benefactors'' is a parable about the perils of an unexamined life. The menage a quartre act and react with great vigor, but with little depth of thought. They are prisoners, therefore, of their self-absorption: Change occurs in their own lives and in the society around them , but they have little grasp of the hows or whys. They simply blow with the wind. As a result, in the end they are none the wiser.

In every sense it is a thoroughly satisfying production. As for the stars, theatergoers will have to seek far to find performances that blend better. And with the recent penchant for stage gimmicks and gadgets, it will remind those who see it just how entertaining an intelligent, well-crafted play - free of frills - can be.