Published: September 24, 1984

In Samuel Beckett's ''All Strange Away,'' a man is imprisoned in a glass cube, a place with no entrance, no exit. The walls are two-way mirrors. The cage is ''all the remaining field for hours of time on earth,'' and the man populates it with memories, pretends to ''paint'' the walls with erotic pictures and clings to his imagination, his fancy, as if it were his mortality.

This brief prose piece was written, the author said, ''on the rocky road'' to an even shorter prose piece, ''Imagination Dead Imagine,'' which was abandoned and then published separately in 1976. Both works share a landscape, language and motifs of light, heat and geometry.

Coincidentally, dramatizations of each have recently been presented in New York, ''Imagination Dead Imagine'' as an actorless holographic tableau by Ruth Maleczech and Linda Hartinian, and ''All Strange Away'' as a monodrama adapted and directed by Gerald Thomas. Mr. Thomas's version, which opened last night at the Samuel Beckett Theater, was seen in an earlier form, with a different solo actor, last January at La Mama.

Mr. Thomas has wisely stripped away artifice he originally added. No longer does the actor preface his monologue by miming simian stances, and later interpolations have also been excised. The new version of ''All Strange Away'' is shorter and less cluttered, focusing on one man's claustrophobic confusion.

In a pitch-dark theater, the cube (designed by Daniela Thomas) shines like a sun, irradiating its own light and revealing, inside, a figure of a man dressed in tatters (Robert Langdon-Lloyd). He is dying but his imagination thrives, playing in tune with the light that falls on his cage. The walls are closing in on him - or he thinks they are - forcing him into a crouch. This is the way the Beckett world ends, not with a cataclysm or a void but with increasingly diminished crawl space under a rotunda.

Mr. Thomas has combed the interior monologue for dialogue. The actor talks to himself, live and on tape. The taped voice is exterior; it oversees the action and in a coup de the^atre, after a blackout, the captive is suddenly replaced by his diabolical captor (the same actor) crouching over a tiny replica of the glass cage, presumably containing the body of the original protagonist in miniature.

At moments, Mr. Langdon-Lloyd, a classically trained actor and a valued member of Peter Brook's troupe, acts too much, fluttering his hands and telegraphing with his eyes. The monodramas of Beckett are best interpreted by the intuitive approach of Billie Whitelaw and David Warrilow, who can chart a clear emotional path through the web of language; with them, words carry the drama. But if we adjust our sights to Mr. Langdon- Lloyd's histrionic style we can receive an ample measure of Beckett's haunting vision, as he describes the ''unappeasable turmoil'' of life in death.

Thriving Imagination ALL STRANGE AWAY, by Samuel Beckett; directed by Gerald Thomas; setting and costume design by Daniela Thomas; lighting design by Howard Thies. Presented by Kilian C. Ganly and the Harold Clurman Theater, Jack Garfein, artistic director. At the Samuel Beckett Theater, 410 West 42d Street. WITH: Robert Langdon-Lloyd