Legally, the case of Daniel James White is closed. Sixteen months ago, the killer of San Francisco Mayor George Moscone and Supervisor Harvey Milk, the city's first openly gay elected politician, was paroled from Soledad Prison. A former supervisor himself, White had served five years and five months for voluntary manslaughter.

Emotionally, however, the case is still wide open. In the minds and hearts of many, White -- the hometown boy and seemingly the embodiment of all virtues red, white and blue, until he muddied the palette by slaying his two political rivals -- literally got away with murder.

"I remember when I first started talking to people about the case -- and this was three years after the fact -- I'd get these incredibly strong reactions. Ferocious reactions. It was like hitting a raw nerve. There was so much rage and pain," says Emily Mann, the author of "Execution of Justice," a documentary play about the trial of Dan White, which begins previews Friday at Arena Stage. Where the rage that once fueled some of the worst rioting in San Francisco's history has cooled, it has been replaced, she believes, by cold cynicism about the judicial system. "That's equally dangerous," she adds.

On one level, "Execution of Justice" is a traditional courtroom drama, drawn from the transcript of the trial, newsreel footage, newspaper accounts and interviews with dozens of the participants. But it is also something bigger and more insidiously disturbing. Jumping back and forth in time, juxtaposing testimony in the courtroom with reaction on the streets, playing one point of view against another, it paints a portrait of a city in agony. While the jury ponders Dan White's crime, the community grapples with the loss of its elected leaders and asks itself not only what happened, but how and why it happened. And where does it go from there?

As Mann says, "This is not a revenge play. In many ways, society itself was on trial -- Dan White's conservative values of family and apple pie versus Moscone and Milk's liberal agenda. What made for an incredibly polarized city continues to divide the country as a whole. We're still working on the issues that were raised in that courtroom."

Mann has devoted four years to "Execution of Justice," researching it, writing it, then whittling away at a manuscript that once would have taken six hours to act. It has already been through two full productions -- one at the Actors Theatre of Louisville a year ago; a second last winter at Center Stage in Baltimore -- and will soon be seen in Seattle, Minneapolis (a production Mann herself will direct) and London. Meanwhile, the script continues to evolve.

"At one point, I bought the radical line of the gay community -- that Harvey Milk was killed because he was gay, a martyr to the cause," she says. "I don't believe that any more. And I used to think that the jury was the key to the trial -- that this conservative, Catholic, working-class, old San Francisco jury would be naturally sympathetic to Dan White, the native son, and take his side.

"Now I don't believe that's what was going on at all. The law was confusing. Dan's [tape-recorded] confession was played in the courtroom and all that raw human emotion coming at the jurors was confusing. In other words, it's very politically and emotionally complex. I think we're really talking about some huge unanswerable human and societal questions."

Liberal and conservative spectators seem to be equally unsettled by the play. "It really is theatrically perverse -- fiercely objective and yet, in its juxtaposition of points of view, totally subjective. Wholly conventional and disturbingly messy," says Douglas Wager, who is directing the Arena production.

It also presents an epic-size challenge with 19 actors in 44 roles, four screens for newsreel footage and multimedia effects, and two live television cameras. Wager says it's "like staging a musical without music." To help the actors find their way through the swirl of events, he recently had them reenact the day of the murders at various sites around town. Each actor followed the itinerary of his real-life counterpart, made the same phone calls and improvised similar conversations. Casey Biggs, who plays Dan White, stayed up most of the previous night, drinking Cokes and gorging himself on Twinkies and the junk food that had become the staples of White's diet. Then, in the morning, arming himself with a stage .38-caliber revolver and a pocketful of blank cartridges, he set out for his prey. By the time the improvisation was over, many of the Arena actors were in tears.

What Wager finds both tantalizing and bewildering about "Execution of Justice" is that "one truth doesn't win out over another. The play merely identifies a trauma -- Dan White's and society's. Emotionally, there's no resolution."

That is, Mann maintains, just as it should be. "I want people to go home and talk to each other about the play, thrash out questions, big questions about our present and our future. What scares me these days is that Ronald Reagan has made us very comfortable with our prejudices. This play really is trying to make us uncomfortable."

In person, Mann seems to bear little kinship to her plays, which are firsthand reports on the walking wounded. The stories she tells are stories she has heard firsthand, often in painful, emotion-wracked detail. As a playwright, she is the confidant of the anguished: the violence-addicted Vietnam veteran, who found his way into "Still Life"; the 74-year-old Jewish woman, whose experiences getting her husband out of a Nazi concentration camp became the basis of "Annulla Allen: The Autobiography of a Survivor"; even the psychologically bludgeoned friends and coworkers of Harvey Milk, who still bleed over his loss.

"I guess people are surprised when they meet me," Mann says. "They picture me as a tough, very intellectual, unattractive, rather difficult older woman."

What they get instead is a slender 33-year-old woman with tousled black hair, faintly bluish circles under her eyes, and the sensual features of a Leslie Caron. If Mann prides herself on her intelligence, it has not been at the expense of a certain coquetry. She is attractive and the generous de'colletage of her summer dress suggests that she knows it. What is most unexpected, however, is her laugh -- which rises and falls like an air raid siren -- and seems incongruous coming from so slight a being.

She grew up in the tony atmosphere of the New England college campus and says with pride that her father, a professor of American history, was the first Jew on the faculty of Smith College (a claim denied by a spokesman for the college). While Mann moved through the world of the Smithies, "all of them wearing their little Peter Pan collars and having their silver teas," the climate was different at home.

"I was raised by intellectuals who had to fight very hard for justice. My father's best friend was John H. Franklin, one of the first black historians to be honored internationally. He was sort of my second father. It was a constant challenge in our house that you had to know what you believed in. A dinner was never a dinner, it couldn't just be fun. There was this whole thing about answering a question with a question. There was never a final answer. You had to continue to scratch away and find all the possible ramifications of the first question you asked, then the second."

Then, too, there were echoes of the Holocaust. Part of her mother's family had been wiped out by the Nazis. "I was always told," Mann says, "that over there -- in what for me was this mythological country -- this is what they did to you. Whenever there was evil in the world, it was always 'like the Nazis.' So we had to know history, know what happened, take responsibility. First of all, because your life could be at stake, but also because nothing like that could ever be allowed to happen again. That was why you were put on Earth."

She still has vivid childhood memories of traveling through Europe one summer, when she was 11. "My sister and I were in the back of the car, as we drove from one town to the next, looking at each piece of architecture along the way, and reading about what happened here in World War II, and then in World War I, and what was this place like in the Middle Ages! My father had bought us a lot of books in England, and as we were heading toward Holland, he gave me 'The Diary of Anne Frank.'

"By the time we got to Amsterdam, I hadn't slept for four days. My sister and I always took showers together, but now as soon as the steam would come out, we'd just stare at one another. In Amsterdam, we'd get into lines for a bus or to go to a movie -- whatever we were doing. And I was certain they were going to call out our names and ask us where we were going. I was such a child! The upshot is, I finally made myself so ill, I never got to Anne Frank's house at all."

A brain specialist once told Mann that her plays have the shape and resonance of "traumatic memory." It is a description she understands and endorses.

"But look, I always had wonderful dates and boyfriends and all that nonsense, too," she says. "I'm not one of those squirrelly girls with glasses. I like to make people laugh, and I was always playing odd, embarrassing tricks on my sister. I was popular in high school. In my freshman year, I was chosen queen of the lab classes. God, how embarrassing!"

From the age of 14, Mann knew she wanted to be part of the theater; all her early inclinations, however, seemed to be toward directing. She passed up Yale Drama School to go to Harvard, although she ended up finding "the theater there sick with young, pretentious types. I really did want to communicate with people and I thought I'd like to do it in rooms that seated more than 100."

On a scholarship, she headed to Minnesota for graduate work and an apprenticeship at the Tyrone Guthrie Theatre. It is there that the Americanization of Emily seems to have occurred. "People kept asking me, 'Where do you come from -- England?' " she says. "So I really tried to get the Midwest accent and laugh a lot and be much more laid back." At the Guthrie, she helped run the theater's experimental wing, and directed many of its productions; wrote her first play, "Annulla," for the Guthrie's leading lady, Barbara Bryne; and also came to know the odd me'nage a trois -- the Vietnam veteran, his traumatized wife, and his lover -- whose violent involvements were the basis for "Still Life," her most widely produced play to date.

It was also at the Guthrie that she met her husband, actor Gerry Bamman, although for the daughter of a history professor she is unforgivably vague on the date of her marriage. "August 1982," she says. "Or was it '81? I can't remember. Anyway, I don't date it from the wedding, that's my problem. Yeah, yeah, yeah, we lived together beforehand! . . . Weddings are very dicey things . . . August 1981. No, I lied. It's '82. God, I can't remember. Don't put it down."

"Still Life" has enjoyed more than 30 productions around the world (it played at Arena Stage in 1983). But the directors of the Eureka Theater in San Francisco were so enthusiastic about it that they promptly asked Mann to write them another play. "They have a socially and politically minded theater, and their tastes are similar to mine," she says. "So I told them, 'Okay. But I don't want to write just any play. I'll write one specifically for your company.' Right away, they suggested the Dan White trial. I supppose if the trial had happened in England, there'd already have been 20 plays on the subject. But nothing had been done here.

"At the time, I had only a slight interest in the subject. It was so much a footnote to Jonestown to me. All I remembered was there had been riots and that San Francisco had gone mad. I knew that Dan White had killed the mayor and somebody gay, or was the mayor gay? And I remembered Twinkies."

" 'The Mayor of Castro Street' [a biography of Harvey Milk] had just been published, so I started to read it. Then I asked them to get me the trial transcript, and I began talking to people. I was amazed at how much was at stake and how important it still was. So I said I'd do it. It was an impossible play to write and I'm still working on it."

The Eureka Theatre was subsequently firebombed, jettisoning the original production of "Execution of Justice," but it is now on the theater's docket for June, a prospect that fills Mann with both a heightened sense of responsibility and a certain foreboding, as well. "I think I'll wear a red wig to the opening," she laughs. "So many people trust me to tell this story with honesty and integrity. If you work in the documentary form and you fail, you don't just fail as an artist. You're letting down people who've put their lives in your hands."

The play's fortunes inspire another thought. "I don't know that I ought to say this in Washington," Mann ventures hesitantly. "But everybody's talking about a national theater these days. Well, it seems to me there is a national theater already -- the collective, nonprofit regional theaters. 'Execution of Justice' is a wonderful illustration of how it works. The idea comes from a tiny nonprofit theater in San Francisco, but they don't have the facility or the money to pull off such a huge work. So Jon Jory picks up on it and does it at the Actors Theatre of Louisville. Because of the Louisville production, Center Stage does it in Baltimore. Doug Wager sees the Baltimore production, and decides he wants to direct the play at Arena. By the time this play gets back to the Eureka Theatre, it will have grown enormously, because four or five wonderful directors, different designers, different companies will all have worked on it. That's the national theater, and it's what we should be proud of."

With "Execution of Justice," Mann's career finally seems to be swinging into high gear -- freeing her from the hand-to-grant existence that has long kept her afloat. She and her husband recently purchased a large Victorian house overlooking the Hudson River in Nyack, N.Y., where they live with their 19-month-old son, Nicholas. Film and TV commissions have started to come in. She's just translated a French play, "Nights and Days," and may direct it this fall for Joseph Papp. The prospect of making ends meet looms ahead.

"Well, I didn't get into the theater because of show business," she says. "I got into it because I thought it was a place where lively ideas are exchanged. Boy, did I have it wrong! But I'm living with my mistake."