Watching a more or less fully clothed couple cavort around a large bed for upwards of two hours has never been my idea of fully satisfying evening, but Jessica Tandy and Hume Cronyn manage to turn this rather barren situation into an enjoyable comedy in The Fourposter. In fact Miss Tandy and Mr. Cronyn are so engaging that one forgets they are involved in what is commonly called "a theatrical tour de force"; aside from the dominantly large fourposter bed which occupies most of the set there is nothing else which remotely resembles a dramatics personae.

The Fourposter is the story of a marriage. It is told in six unrelated scenes which take place at crucial points of the marriage and in which Mr. Cronyn's hair grows progressively thinner and his wife's grayer. The standard stagecraft is complemented by standard situations: the wedding night, the first child, the other woman, the wayward children, and the realization of age are the incidents on which the scenes are built.

What saves The Fourposter from what might have been its expected fate--critical curses of "static" and "trite"--is author Jan de Hartog's plausibly witty dialogue and believably gradual development of character. He has made things easier for his audience by casting his male lead in the part of an author of best selling if not memorable novels. Thus Mr. Cronyn can be humorously sarcastic without imposing on the audience's credulity; his lines are what one might expect from a clever, superficial writer. As his wife, Miss Tandy progresses from a blushing but eager bride to a mature woman without any false crises. Rather her growth can be seen in the way she addresses her husband, her taste in clothes, and her manner of walking.

What faults the play does have are due in the main to its unnaturally restricted setting. With no comic maids, noisy children, or boisterous relatives to lives things up, dc Hartog has attempted to provide a touch of raucous humor by a truly banal bit of stage trickery--a raised platform around the bed over which either one or both of the characters is prone to stumble in moments of passion or tenderness. This sort of thing is good for a yuk the first time, but after the third repetition even the fellers and gals of the John Hancock Life Insurance Company, which had bought out the orchestra the night I saw the play, began to react a bit slowly.