You don't want to judge ''The Petition'' by its first act. All sorts of questions arise during the opening act, questions that need to be answered.
The questions, it turns out, are answered during the second act, to the relative satisfaction of the viewer, and by the time the play is ended, we are pleased to have been in the company of an interesting couple.
Of course, the couple in "The Petition" are a little exasperating, but then they are British aristocracy, and these people have always marched to their own classical music, if the plays and movies that have been written about them are in any way accurate.
''The Petition'' is being very nicely done at the Olney Theater. Mark Hammer and Ruby Holbrook are the principal and only characters on view. He is a retired general who has passed his 80th birthday. She is Lady Elizabeth, who is somewhere in her early 70s.
If we are to judge them only by the first act, they seem unusually non-communicative. They have been married more than 50 years and have raised four children, but they don't really seem to know that much about each other.
The second act may explain why. She had, at one point, engaged in a two-year extramarital affair, which may be the reason for their reticence. The marriage may be more truce than compatibility.
He always knew about her infidelity but stood by her. This is a man who may strike some as silly when he talks about war. Like the airmen of World War II, he looks on it as a kind of game, a sport in which it is good form to congratulate the enemy on his bravery.
The general is, however, extremely admirable in the marital department. Not too many men would have put up with what he has put up with.
The play, done on Broadway a few years ago with Jessica Tandy and Hume Cronyn starring, takes place in the living room of the Milne home. He drinks too much, and she is apparently ill. She's had an operation, so we begin to suspect that all has not gone too well.
In fact, it hasn't. And when she tells her husband, he is, once more, most admirable.
The original premise is almost superfluous, but it does serve to get the play going. She has, in her advanced years, signed a petition calling for the ban of first-strike nuclear war.
She seems a little too old to be doing this sort of thing, and one of the questions that arises in that first act is why would she bother? The question also occurs to the husband, who, in the second act, asks his wife why she waited so long to act. ''You could have done this many years ago,'' he says. ''That's why I cannot take it too seriously.''
She is also off-hand about the French. ''So they had a bad five years,'' she says, referring to the French participation in World War II.
The performers are every bit as good at their material as their Broadway counterparts. They may even be a bit better. We believe these people more than we want to because the actors make them more appealing, perhaps, than they really are.
''The Petition'' was written by Brian Clark, author of ''Whose Life Is It Anyway?'' It's a small thing, made to look bigger at the Olney, where it will remain through June 30.
Jack Going did the direction, and James Wolk did the very appropriate set.
''The Petition'' ** A retired general and his wife learn something more about each other.
CAST: Mark Hammer, Ruby Holbrook
DIRECTOR: Jack Going
L RUNNING TIME: One hour and 40 minutes with one intermission.
! TICKETS: 924-3400