What happens when an atomic bomb moves next door. Also: Vienna's pleasure seekers; a writer's checkered career

Trinity Site Play by Janeice Scarbrough. Directed by William Ludel. ``Trinity Site,'' at the WPA Theater, seeks to dramatize the effects of a catclysmic event on the everyday lives of a New Mexico ranch family. Janeice Scarbrough takes her title from the code name for the 1945 bomb test at the Alamogordo Air Base. As the play opens, the Hobart family is as unaware as the rest of the world of what is about to take place. They are preoccupied with the usual round of ranch and domestic concerns plus the worry of what may have happened to Lanell Hobart's brother, who is with the armed forces in the Pacific.

The routines of a hot summer day are interrupted by the arrival of a deceptively casual stranger named Ingram (Christopher Curry), who asks directions and indicates an interest in buying land in the neighborhood.

Admitting that his interest bears on the war effort, Ingram ultimately induces Marshall and Lanell (Mark Metcalf and Patricia Richardson) to let the government purchase most of their property. Inner domestic tensions surface in the course of the transaction and its aftermath. Time tends to hang heavy, as the playwright prepares the ground for the climactic blast and its effects on the Hobarts. Lanell's miscarriage, brought on by the explosion, is but the most poignant physical result of the family's ordeal.

Miss Scarbrough leaves the Hobarts as they go about the painful task of putting their lives back together. But life at Trinity Site will never be quite the same. Being a part of history has taken its toll.

That the intent of ``Trinity Site'' exceeds its achievement is not for want of earnest effort. The Hobarts -- including Royana Black as teen-age daughter Dale -- are believably acted under William Ludel's direction. Mr. Curry does perhaps more than might be expected with Ingram, the government man whose attempted explanations after the fact do not placate the previously trusting Hobarts. As usual with the WPA, the production has been well designed, with sets by Edward T. Gianfrancesco, lighting by Phil Monat, and costumes by Don Newcomb. The play is scheduled to run through June 29. Vienna: Lusthaus Performance piece conceived and directed by Martha Clarke. Text by Charles Mee Jr.

A well disciplined company of performing artists dances and prances, glides and slides, writhes and slithers through the paces of ``Vienna: Lusthaus,'' at the Public/Newman Theater. Martha Clarke's dreamlike series of set pieces, dance movements, and tableaux vivants evoke the social behavior and carnal misbehavior of Viennese pleasure seekers near the turn of the century. Still life and action intersperse with Charles Mee Jr.'s bizarre and surreal texts, recited deadpan by the speaking members of the ensemble. Instrumental soloists and a solo singer (guest performer Lotte Goslar) take the stage from time to time. The integral musical score was composed by Richard Peaslee, with acknowledged assists from Johann Sebastian Bach, Eugene Friesen, and Johann Strauss. (``I don't like Johann Strauss,'' complains a dissenter at one point.)

Whatever its explicit eroticism, ``Vienna: Lusthaus'' is formally composed and, except for occasional attempts at comedy, austerely presented. The performance takes place behind a scrim with which set-and-costume designer Robert Israel achieves a remote, distancing effect. Paul Gallo's lighting, with its subtle shades and bold shadows, enhances the mood. Snow falls and so, at last, does one of Miss Clarke's smartly uniformed officer types, as a wintry chill settles over the pleasure gardens where these worldlings disport themselves.

Physical imagery (including nudity) and the flow of movement serve as Miss Clarke's means of capturing and captivating the spectator. For those who agree with its favorable critical reception, ``Vienna: Lusthaus'' may well prove visually enchanting and enigmatically fascinating. The less favorably disposed may find the experience precious, pretentious, and somewhat pointless. What is it about? To borrow an old gag, about 65 minutes. Performances are scheduled to continue until June 26. Writer's Cramp ``An entertainment in two acts'' by John Byrne. Directed by David Kerry Heefner.

John Byrne's ``The Slab Boys'' won a deserved Off Broadway welcome at the Hudson Guild Theatre in 1980. (It later had a brief Broadway run.) The Hudson Guild is now presenting the New York premi`ere of Mr. Byrne's first play. Originally performed in Edinburgh in 1977, ``Writer's Cramp'' chronicles the checkered career of fictitious Francis Seneca McDade (1917-1976). Mr. Byrne depicts McDade as a Scottish hack writer, briefly acclaimed painter, and full-time cadger.

The play opens with a local literary society tribute to McDade by two of his most ardent fans, one of whom credits their hero's ``Feet of Clay'' with having launched ``a new epoch in Caledonian culture.'' The encomiums are interspersed with excerpts from McDade's voluminous letters and with flashbacks recalling his adventures at boarding school and Oxford, in the army and wartime prison (his natural father was a German), and his brief bout with fame.

K. C. Kelly endows McDade with a suitable air of obtuse self-confidence and a heathery Scots burr. The lampoon requires Sullivan Brown and Brooks Baldwin (the effusive McDadites) to demonstrate their versatility in a variety of caricatures (once each in drag).

As presented at the Hudson Guild, however, ``Writer's Cramp'' suggests an over-extended Monty Python vaudeville, staged with a far from light touch by David Kerry Heefner. Richard Harmon designed and lighted the dingy setting for ``a small meeting hall in Scotland -- and beyond.'' Patricia Adshead's costumes include some antic get-ups.