Alan Ayckbourn's "How the Other Half Loves" is squarely in the British tradition of bedroom farce: a lot of dainty japing about sex, plus a giggly fascination with the loo. The Round House Theater's show, cluttered by such rubbish, isn't otherwise half bad.

This Americanized version, about New York instead of London, concerns adultery and suspicion among executives and their wives. In theatrical "split-screen," the action happens on a pie-sliced set, with the well-to- do Fosters and upwardly mobile Philipses ensconced -- simultaneously -- in their lairs.

The dull-witted Detweilers, who round out the story's intra-office menage, visit both couples now and then to serve as comic foils. Director Jeffrey B. Davis and scene designer Douglas A. Cumming have choreographed the gimmick with a measure of grace -- even in a time-bending scene that has Detweilers dining with Fosters and Philipses on different nights, but at once. The acting doesn't stumble too badly, either.

Though foolish fluff of late-'60s vintage, the show has laughs -- many of them supplied by Sarah Marshall as mousy Mary Detweiler, the witless victim of an affair between middle-manager Bob Phillips and his boss' wife, Fiona Foster. By muddled means, she becomes a prime suspect. From half- hearted mutter (as guest of the imperious Fiona) to full-blooded scream (at her husband's dangerous wrath), Marshall shows a funny flair unmatched by her colleagues. She also works well with Mark Jaster as her meek spouse, William, her moony looks lending his prissiness a ridiculously heroic stature.

To the role of Frank Foster, blind to his cuckolding, Michael Littman brings avuncular good cheer but no authority. Spouting oily platitudes like the mindless "Nice to have seen you," he seems such a silly no-account that when he presents his untied shoelaces to his underling Detweiler for action, the laugh's not there. Anne Stone has more of the required bite as the bitchy Fiona.

Greta Lambert and Gerry Paone seem a tad too solid as the Philipses, their squabbles more like "A Streetcar Named Desire" than the light-headed matter at hand. HOW THE OTHER HALF LOVES -- At the Roundhouse through December 12.