Hugh Leonard's "Stephen D" is even more impressive in the Hartke Theater's new production than it was at its Olney bow a dozen years ago. With Jarlath Conroy, as guest artist, quickening the Catholic University students, the run resumes tonight to play through Feb. 12.

Leonard created the play by adapting James Joyce's words from "A Portrait of the Artist as a Young Man" and "Stephen Hero." So deftly did Leonard use the stream-of-consciousness technique of Joyce that there is an inevitability of form and event in detailing the spiritual questing of Stephen Dedalus.

Joyce traced his personal rebellion through Stephen D., whom we meet as a boy in 1882 and leave as a young man departing from Ireland 20 years later. At first he observed his family, their beliefs and actions. Then he began to question. Finally he accepted disbelief and its consequences. Leonard's contribution is this dramatic line - a beginning, a middle and an end.

The thinking is Joyce's, what he grew to regard as the bigotry and hypocrisy of his Irish Catholic background. Reliving the events of his youth during his lifelong exile to Paris, Joyce limited his scope but dug the more deeply, with the striking result that he widened that scope's ramifications. Thus, the self-portrait achieves a universality beyond Ireland; Stephen is Everyman striving to think for himself.

A further reason for the play's deepened impression possibly is that Vatican II still had not shown its effects when the play appeared. Pope John's "aggiornamento," or modernizing, was a phrase that took some years to implement. At least some of Joyce's criticisms - and those of others - influenced the thinking of a half-century later.

Finally, there is the writing of Joyce: precise, regretful, ruthless, humorous and flashing. His perceptions of character in his family, his teachers, the clergy and his fellow students create individuality for them all.

These give the large cast vignettes to which many rise with almost surprising assurance: Mary Koumjian's Mrs. Dedalus; Laura Giannarelli's Dante; Robert Lesko's Mr. Dedalus; Jack Hrkach's Uncle Charles; and Paul Rubin, Tony Ginter, Michael Barbour, Tony Reich, Tom Aldridge and Justin Lombardo as a whole range of clergy. Ed Bourgeois is especially arresting as Cranly, Stephen's most perceptive friend.

Irish-born, British-trained and admired on Broadway, at Olney and Arena. Conroy is splendidly thorough as Stephen, serving as narrator, protagonist and source of strength to all, again vindicating the university's use of guest professionals. Rolf Beyer's setting and the technical details complete a fine, finished production, an absorbing theater experience for all.