In marriage as in life, says therapist Adi Shmueli, "small things often make the big difference.

"Amid the pressures of daily routine, minor problems occur that don't get resolved. Couples get stuck in systems of interaction. Things fester."

Failure to detect and defuse these "land mines" usually results--sooner or later--in "a blowup." While couples are often blind to their own potentially destructive patterns, "they're much easier to recognize," he says, "in other people."

To help couples reflect more clearly on their own relationships, Shmueli, who has a private practice in the District, and his wife Iris, an NIH clinical social worker, decided to set up a dramatic mirror.

It's called Marriage Theatre, a series of five one-act plays--each highlighting a common marital conflict--followed by audience discussion. Starring Shmueli, 42, who "did a little acting in high school and college," and professional actress Cappy Lyons, the performances are directed by George Washington University drama professor Nathan Garner.

The first play--"Why Don't You Ever Put Me First?"--debuted to capacity audiences of about 100 last Friday and Saturday night in the Washington Hilton's Hemisphere Room.

During the post-play exchange--led by Shmueli--a man in the front row summed up the performance like this:

"That could have been any one of us up there. The characters were probably once loving and kind, but what I saw was two people who probably let the pressures of day-to-day life get to them. Each was asking the other, in their own way, for love and recognition. When they didn't get it they reacted with hostility."

The audience was mainly couples; most checked "professional" as their occupation and "35--49" as their age group. "We were thrilled at the response," admits Iris Shmueli, 41. "We'd been scared to death that no one would come."

The idea for the marriage theater, say the Shmuelis, was born of their frustration in explaining complex relationships through traditional ways like books and therapy. They spent six months and nearly $50,000 isolating marriage's most private moments for portrayal in a public arena.

When Adi Shmueli first started exploring the concept last fall of "acting out certain conflicts in front of groups, some people looked at me like I was crazy. But I really believed there was a yearning for this kind of intellectual exchange. People are very curious and they want to do more than sit passively. Many have a thirst for this kind of thoughtful discussion without the threatening context of therapy or academia.

"When you watch a play and discuss how the characters related you talk about yourself without getting too personal."

Although the Shmuelis stress that no two marriages are alike, they define these basic conflicts as central to marital discord, thus the themes for the five Marriage Theatre plays:

* Dependence vs. Independence. "You Think You Know It All": a "benevolent dictator" husband and a "squashed" wife.

* Mutual Neglect. "Why Don't You Ever Put Me First?": what happens when people get so busy with their public lives that they forget each other.

* Opposites Attract/Repel. "The Mad Passionate Fool": how we look for our opposite, then spend the rest of our life trying to change them into ourselves.

* Different World Views. "Great Expectations": the problems that arise when couples from different cultures don't communicate what they want from one another.

* Fear of Rejection. "Who's in Charge Here?:" a liberated couple who confuse being equal with being the same.

"Our hope," says Adi Shmueli, "is that people will return home softened, mellowed. Partly because the theater is a way to break through loneliness, to see how much we all share. Also, none of these plays have a good guy and a bad guy. There is no black and white . . . which I find very encouraging."

Shmueli's view that "life is neither here nor there but in the middle somewhere," is rooted in his first career as a philosopher. Born in Baghdad, he moved to Israel at age 9, received his masters in philosophy from Tel Aviv University--where he also taught--and his doctorate from the University of Tours in France.

In 1970 he "felt the need to come closer to life," and moved to New York to earn a second doctorate, in psychology, at the University of Rochester. There he met his future wife, a Texas-born former nurse practicing clinical social work. They married and moved to Washington in 1976 after a visit during Cherry Blossom time impressed them with the beauty of "this very European city."

In a decade of working with couples, Shmueli has concluded, "staying married until death do us part is a lot harder now than it used to be. When the Bible was written, people lived 25, maybe 30 years. So marriage for life was altogether a different story.

"Now two people get married and 10 years or 20 years or 30 years later they've changed. They may still be together, but they're different people. When things get difficult there can be a desire to hurriedly run, to throw away that spouse and find another."

But there's "a heroism," he contends, "in remaining married despite the difficulties. We want to help people reach deep to discover untapped resources and uncover new possibilities for growth and happiness to keep love alive."

The current Marriage Theatre series continues weekends through April 9 and will be repeated April 15 to May 21. Single tickets are $12; two to four tickets, $10 each; five or more, $8. For more information: 463-8217. Acting It Out

In the debut production of Marriage Theatre -- Why Don't You Ever Put Me First?"--Al and Vicki battle over their 15-year-old son's attendance at a family function.

Vicki: Can't you see how you're undermining me? David is learning from you not to pay attention to me, his mother.

Al: Stop talking about attention all the time. You don't pay atttention to me either.

Vicki: Now what is that supposed to mean? You mean I don't cook for you? You mean you never have clean underwear?

Al: You don't understand. You don't pay attention to me, to me. I am not talking about food or underwear. I'm talking about me.

Vicki: My God, I take care of everything and everybody in this house. What else do you want?

Al: Yes, you are Mrs. Dutyfirst. You take care of everything here. But you never pay attention to me. What do you know about how I feel at work? What do you know about my problems? Every time I mention my work you tell me to shut up.

Vicki: You are lying. I never told you to shut up.

Al: You tell me that I shouldn't complain, that everybody in the world has to work. It's the same thing as telling me to shut up, just a bit more refined.

Vicki: Look, I think you had a bad day at work and you are taking it out on me.

Al: You see, you're doing it right now. You're basically telling me to shut up.

Vicki: I'm not telling you to shut up. I'm only saying that you are angry at your boss and you are taking it out on me. You came home geared up for a fight, and you were going to find something to fight over. It has nothing to do with me.

Al: Well, hell! Right now I'm not angry at my boss, I am angry at you, at you, at you!

Vicki: Hey look, can we shelve this right now? You are angry at me, that's okay. But right now we have to go to my mother.

Al: Look, I say I'm angry and you say it's okay. I am not going to your mother's.

Vicki: What do you mean?

Al: You heard me. I am not going to your mother's. I am going to watch TV the entire evening.

Vicki: No you won't.

Al: You bet I will. The TV is the only thing in this house that I touch and it responds.