WHEN ROBERT CHAPMAN directed his freshman seminar candidates to read 25 lines of script in their interviews last September, few knew what they were in for. First there was the month of kabuki, the weeks of mime, the scattered gymnastics. But tonight and tomorrow Chapman's band of recently-removed high school stars and latent freshman talents converge at the Ex to vent their acting frustrations in the culmination of the course.

The group hunted hard to find a play equally accommodating to its fourteen members. After a prolonged search they gave up and settled for a snatch of Shaw-the second act of Major Barbara-and a tantalizing Sam Shepard encounter session, Icarus' Mother.

Surprisingly, director Chapman meshes the decapitated Shaw and the frenetic Shepard well. Of course adjusting to a sliced-up play is difficult. For an audience, it is almost like walking in on an already erupted party. But the actors make warm hosts, so breaking the ice takes just a few minutes. What unfolds is a perverse look at the Salvation Army, complete with its misfits, military hierarchy and loathesome benefactors.

The action is a bit shaky at first. A drawn-out scene introducing a band of "shiftless and lazy" characters is relatively unappealing. But the entrance of the skeptical Bill Walker, played with comic gusto by Dan Beckhard, threatens to shake the charitable base of the conversion-oriented mission. Beckhard acts as a conductor, setting the other characters on fire. They ignite at his caustic brutalizing of the mission's sacharine Jenny Hill.

His machinations hasten the entrance of Major Barbara. The comforting commander, made even more soothing by Ellen Anderman's empathetic performance, douses the raging Beckhard. But the arrival of the play's two strongest characters-Cousins, Barbara's boyfriend, and Undershaft, her father-threatens, and eventually undermines Anderson's moderating role.

Chapman's directorial talents emerge as he harnesses the brute power of the hulking Jon Epstein. The director bottles Epstein into the cold and calculating Undershaft of this second act. In this section we hate this mild-mannered munitions manufacturer who wants to donate his blood-stained profits to the sweet cause of salvation.

Chapman also channels the talents of John Majors into a penetrating Cousin, who accentuates Undershaft's demonical doctrines as he confronts him. Once Majors conquers his inappropriate Trotsky-like appearance and stops pounding his irritating drum, there ensues a battle which erases any doubt that Undershaft might not be "an infernal old rascal." As the single act draws to a close and Ellen Anderman unconvincingly projects Major Barbara's breakdown, the lingering image of the triumphant Undershaft provides a good conclusion for a play left in mid-air.

CHAPMAN DOES not seem to maintain the same sure footing in Shephard's Icarus. Certainly his vast knowledge of Shaw overshadows this less conventional play, so that the result is a less polished product. But this bizarre Shepard play, with its plot based solely on conversational interactions between its characters, fits snugly into the theatre-in-the-round setting. The five characters work quickly but too loosely, relying on a casualness that often lets the show get by as a friendly get-together rather than a plausible dramatic situation. The intital comedy, evolving around a buzzing airplane, establishes Andy Rosann's Bill as the comic of the group-the man who creates the funniest gags, and makes the even funnier gestures. Gradually the rest of the cookout's participants warm up to Bill's level with Cindy Cardon's Pat and Lorenzo Mariani's Howard forming a chilling team of innocence and brutality.

The actors eventually reveal a desire to see some greatly anticipated fireworks-a pyrotechnical display that Bill insists be seen by the whole group. His insistence, coupled with the desires of Pat and Pam Stone's Jill to separate from the group, provide the degree of conflict necessary for the rest of the play's actions. Meanwhile, on the periphery, Jerry Colker beachcombs his way through the role of Frank, who joins Pat's and Jill's dissension, which leads to the destruction of the five's opening cameraderie.

In turn each character receives air time for a few minutes of monologue, of which Rosann's was most impressive. The glib prankster has the timing of a well-practiced magician; he turns banal lines into comic magic. Cardon and Stone have their moments too, especially when they alternate in reciting a tale of their unexpected urge to relieve themselves on the wide-open beach.

But Shepard's play is a difficult one to transform, and an even more difficult one to watch. One can enjoy the intervals of comedy and relish certain moments of dialogue, but even perfect execution wouldn't lend clarification to Shephard's meaning.

It doesn't work as well as Barbara, but it does fulfill its role as an intriguing end to an enjoyable double-billing. One's only regret at the finish of the night, is that Chapman did not unleash his students more often. But with the limited amount of time that he budgeted these two plays in his overall course program it appears that if Chapman had had his way there might be no freshman seminar production at all. This type of performance, however, even if it is a simple by-product of a year's "academic" work, is worth retaining, if not for the course's participants, than at least for the audience's delight.