Beckett trio is brief but absorbing; Ohio Impromptu, Catastrophe, What Where Three plays by Samuel Beckett. Directed by Alan Schneider.

A Samuel Beckett triple bill - two world premieres and a New York first - comprises the brief but absorbingly intense dramatic fare now being performed at the Harold Clurman Theatre. Except for the central piece, the plays are scarcely more than fragments, testaments to human vulnerability, reminders of man's inhumanity to man amid the presence of death. Death itself can be physical or spiritual, no matter what Godot Beckett's man may be awaiting.

''Ohio Impromptu,'' first performed at Ohio State University in 1981, is a poignant tale of love and separation unfolded by the Reader (David Warrilow) to the Listener (Rand Mitchell), a silently impassive image figure. The identical white-haired, white-bearded men sit at a table. Action is minimal: the turning of a page, the Listener's occasional impatient rapping of the table. In tone, if not in content, the mood recalls the quiet sorrow of ''Krapp's Last Tape.'' Mr. Warrilow's reading is beautifully modulated, his voice the sensitive medium for the tale's sorrowful message.

In the central play - dedicated to Vaclav Havel, the dissident Czech writer - Beckett delivers a stinging indictment of the communist totalitarianism that oppresses and suppresses its artists. The title, ''Catastrophe,'' is here given the French pronounciation, with the accent on the ''stroph,'' which somehow makes the implication seem more catastrophic.

In this polemical satire, a commissarlike Director (Donald Davis) gives imperious instructions to his Assistant (Margaret Reed) as she arranges a silent and shivering Protagonist (David Warrilow) for the event of the title. Mr. Davis's Director, with his fur hat, fur-trimmed coat, and big cigar, is the quintessential petty tyrant of dictatorship. White-coated Miss Reed personifies the immemorial note and order taker, the faceless factotum without whom dictatorship could not function. Mr. Warrilow as the subject-victim of ''Catastrophe'' recalls in some respects the struggling Lucky of ''Waiting for Godot.''

The evening concludes with ''What Where,'' described as a play of ''terror and inquisition.'' Four characters, clad in long white robes suggesting both timelessness and antiquity, engage in a series of cruel interrogations. For refusing to reveal the desired but unspecified information, the victim is threatened with ''the works.'' The torture, which occurs offstage and is merely reported, ceases when the individual being questioned passes out.

Considering the widespread employment of such brutal methods reported by Amnesty International, it is not surprising that director Alan Schneider considers this searing playlet ''one of Beckett's most political dramas.'' The mythic, interchangeable characters in the ''What Where'' realm of terror are Bam , Bom, Bim, and Bem - played respectively by Mr. Davis, Mr. Warrilow, Mr. Mitchell, and Daniel Wirth.

Although the tone of the evening is prevailingly dark and somber, Beckett does allow himself some comic and satirical touches in ''Catastrophe.'' At one point, for instance, the Director protests impatiently against ''this craze for explication.'' The protest could be directed equally at impervious bureaucracies - or at some of the playwright's critics.

The performance staged by Mr. Schneider is meticulous in detail and dedicated in spirit. The acting is fine throughout.