I wish you'd lied to me."

Jeffrey Sweet regarded this line from his play "Porch" as his version of the Tennessee Williams line, "I have always depended on the kindness of strangers" in "A Streetcar Named Desire." It was to be the line that tied up the play in a way people wouldn't forget. One for the books. In fact, it had was published in "The Best Short Plays 1976" before it was ever staged.

When Sweet brought "Porch" here for Arena Stage's "In the Process" program, in which plays are constantly rewritten, he knew that at least he had one line to depend on. "There was no chance I was going to change it," he said.

That was several weeks ago.After the first performance of "Porch" for an audience last weekend, it became clear that not everyone understood Sweet's favorite line. It was time for a change, he acknowledged. Two candidates were nominated as possible replacements: "I wish you could have lied to me" and "I wish you could lie to me." Audiences at Area tonight will learn the identity of the winner.

Artists are often seen as solitary figures who don't really care what their audience thinks. If others appreciate them, fine; if others don't, maybe posterity will.

But the fact is that if today's audience doesn't appreciate your work, tomorrow's may never get the chance. So most artists fiddle with their initial visions until at least someone, somewhere, understands and likes what they're doing.

This fiddling becomes big business when it's done to commercially oriented scripts. Consumer taste tests are conducted: In the theater they're known as "tryouts" or "previews," in the movies as "sneak previews." In commercial television, shows are screened for people whose pulses and heartbeats are scientifically monitored. If your creation flunks these tests, it's curtains. Or that's the way it usually seems when big money and quick deadlines are involved.

The harrowing experiences of writers who go through such experiments are legendary. Noncommercial theaters like Arena Stage eliminate most of that hassle. Still, most producers and writers hope for a degree of compatibility between audience and production. Last year Arena started "In the Process," a playwriting laboratory equipped with audience and professional cast and crew, where writers can control their own experiments, can even flunk audience tests with reckless abandon. Audience responses are used to nurture the plays, not to make or break them. Deadlines are minimized. There's no big money but there's enough little money to get by. It's not the proverbial bigtime, but it's a possible way to get there without cracking up.

Tonight the second session of the second season of "In the Process" ends. This was the first time more than one playwright was involved at one time. A company of four actors and two directors presented three one-act plays - Sweet's "Porch," Janet Neipris's "Exhibition" and Richard Nelson's "Scooping" - at a rate of two plays per performance. The last nine performances in the 165-seat Old Vat Room were in front of paying audiences, mainly Arena subscribers, who bought all available seats before the season began last month.

The playwrights watched their audiences carefully. Sweet compares the experience to listening to stereo - on one channel he followed the action on stage, on the other he devoted equal attention to what's going on in the audience, particularly "when chairs squeak or people cough."

"You can really feel the audience trying," says Janet Neipris. Thomas Gruenewald, who directed the Neipris and Sweet plays, says he can feel the playwrights trying, too - Sweet grabbing his arm when the actors made "a little ellipsis," Neipris gesturing in the dark as she mentally rehashed difficult passages even as the actors had moved on.

After the performances the authors and directors lead an audience discussion of their work. Professional critics are not allowed to write a word, so the amateurs take over, analyzing and arguing and offering suggestions about what they have seen. Written comments are invited on the backs of the programs.

Despite their enthusiastic participation, audiences should know that they are really serving as guinea pigs. Scripts are changed daily, and some versions are clearly more thrilling than others. The playwrights are more interested in general responses - did it work? - than in specific suggestions from the audience.

Specific ways to improve the plays are uncovered in the rehearsals. Actors suggest changes without feeling like time-wasting prima donnas. Directors direct without worrying about critics and backers. Playwrights preside over everything that happens to their scripts without feeling like "pests" - Sweet's characterization of the way playwrights frequently are treated at rehearsals.

The only possible source of career pressure comes from the fact that Zelda Fichandler, Arena's producing director and someone who might select a playwright's work for a full-scale production, originated "In the Process" and is there to observe what's going on. But Fichandler says not to worry: The "freedome to fail" is part of the process. Her main goal is giving the playwright "a sense of what it feels like, kinesthetically, to work well."

"To work well" means a lot to a playwright. It means to earn a living, for one thing. Nelson says that in the last four years of writing plays, he has earned $900 (and that includes two professionally staged plays and seven aired radio plays). Here he receives $15 a day, 1.5 per cent of the gross, an apartment and transportation to and from Washington.

It's no way to get rich, but it could amount to more than half of that $900 from his last four years.

"Working well" also has a psychological meaning. Most playwrights "sit in their apartments and write for four walls and hope the brown envelope reaches the right eyes," says "In the Process" coordinator Douglas Wager. The six plays seen "In the Process" this season were selected by Fichandler from 70 such envelopes. Once selected, though, the "Process" playwright works in a professional theater, as the most important member of the company. It gives a playwright "confidence," says Sweet. "We all want to have a home," says Neipris.

Nelson believes playwrights should be on theater payrolls. Joseph Papp has hired some in New York. Fichandler disagrees, insisting "it's always better to start with something on paper" and warning that a salaried playwright would "have to be careful of the implicit bondage" to a producer or theater. (Playwright Christopher Durang will be in residence at Arena later this season, but his residency started with "something on paper," - Arena will present his "A History of the American Film." His stay will be financed by a special $12,000 grant from the Rockefeller Foundation.) Fichandler does think playwrights deserve better treatment and says "In the Process" is "a modest step" in that direction.

Not all "Process" playwrights have treasured every moment, but the three who will leave after today certainly seem contented. Away from the usual pressures of a playwright's existence, Janet Neipris says she has "never been so happy working in all my life." Never, she says, "had I spent the last hour before opening night curtain in a supermarket buying a carton of milk."