The voice from history is that of John Wilkes Booth, the assassin of President Abraham Lincoln, and the scene from 1865, with music and lyrics by Stephen Sondheim, is being re-created eight times a week on the main stage of Playwrights Horizons, a nonprofit Off Broadway theater company on West 42d Street in New York City.

The credo of an American Presidential assassin is hardly your usual musical-theater fare. But then again, this musical is not about an American Presidential assassin. It is about nine of them -- nine assassins or would-be assassins, nine bizarre, destructive and demented people. It is titled, appropriately enough, "Assassins." It is directed by Jerry Zaks ("Anything Goes," "Six Degrees of Separation"), with a book by John Weidman (who collaborated with Mr. Sondheim on "Pacific Overtures" in 1976), and it opens officially tonight.

"There are always people who think that certain subjects are not right for musicals," Mr. Sondheim says, sitting with Mr. Weidman and Mr. Zaks in the director's office on West 44th Street. "I remember that there was a letter of protest when Rodgers and Hammerstein's 'South Pacific' opened that said, 'How dare they write a musical about miscegenation?' 'South Pacific' hardly seems like a shocker today, but it was in 1949. There were people who were horrified that such a serious and upsetting subject as interracial marriage should be dealt with by the most popular musical writers of the day."

He turns to Mr. Weidman, who nods in assent. "We're not going to apologize for dealing with such a volatile subject," Mr. Sondheim says. "Nowadays, virtually everything goes."

"Assassins," constructed in a form somewhere in the twilight zone between book musical and all-star revue, tells the story of those nine people, who, through madness or political conviction, or both, too often succeeded in changing the course of history and bringing immense pain to the world. But the 90-minute musical, presented with no intermission, is not meant to be a simple history lesson; it has a surreal quality, created largely by scenes in which the assassins from different eras meet one another.

In addition to Booth, the assassins and would-be assassins are Charles Guiteau, who killed James Garfield; Leon Czolgosz, who murdered William McKinley; Giuseppe Zangara, who tried to kill President-elect Franklin D. Roosevelt; Lee Harvey Oswald, who assassinated John F. Kennedy; Samuel Byck, who tried to kill Richard M. Nixon; Lynette (Squeaky) Fromme and Sara Jane Moore, who shot at Gerald Ford, and John Hinckley, who shot Ronald Reagan.

Crossing the lines of time and space, the assassins talk and sing to one another, accompanied by a three-member orchestra. They meet at a carnival booth, where the faces of former Chief Executives roll by and a barker exhorts them to step right up and kill a President. They taunt, they commiserate, they laugh, they explain themselves with both pride and angst, and they engage in what can only be termed very dark humor. Fromme meets Hinckley; Booth talks with Oswald; Guiteau instructs Moore; they all gather over drinks at a bar. They sing as a chorus. Woven through the evening are historical drawings and photographs, as well as another character, a balladeer, who presents folklike songs about the killers.

But amid the surrealism there is reality, at times an insane reality. "One of the things we would like to emphasize is that the vast majority of the actual details of the show are true," Mr. Sondheim says. "I don't want to give them away, but there are so many bizarre things."

Featuring a cast of 16 that includes Victor Garber as Booth, Jonathan Hadary as Guiteau and Terrence Mann as Czolgosz, the musical began preview performances Dec. 18 in Playwrights Horizons' 139-seat main theater. The production, which is scheduled to close Feb. 16, is sold out. The only tickets available are from last-minute cancellations. There is also the possibility of an extension and perhaps, depending in part on the critical response, a transfer to a commercial Broadway or Off Broadway run.

Tackling difficult and provocative material is not unusual for Mr. Sondheim and his various collaborators. "Sweeney Todd," after all, told the tale of the Demon Barber of Fleet Street, a gruesome killer who dispatched his victims in Victorian England amid the horrors of the Industrial Revolution. "Pacific Overtures" took as its subject the forcible opening of Japan to the West in 1853.

Mr. Sondheim's breakthrough musical, "Company," dealt with the tangle of male-female relationships; "Sunday in the Park With George" examined the nature of creativity and art, and "Follies" investigated, through metaphor, the disintegration of American society after World War II. As early as 1964, two years after "A Funny Thing Happened on the Way to the Forum," the first Broadway show for which Mr. Sondheim wrote both music and lyrics, he and Arthur Laurents created "Anyone Can Whistle," a musical in which patients escape from a mental hospital and mingle with tourists in a small town.

So when Mr. Sondheim first encountered the idea of a musical about assassins, it is not surprising that he was fascinated, just as throughout history many nonmusical writers have been fascinated about the mind of the assassin, from the motivations of Brutus to the machinations of Lee Harvey Oswald.

It all began, Mr. Sondheim says, about a decade ago, when the producer Stuart Ostrow formed something called the Musical Theater Lab, which was devoted to finding and encouraging new work. There was a panel of several composers and songwriters, and one script that came across the desk, written by a man named Charles Gilbert, was called "Assassins."

"I looked at the title," Mr. Sondheim says, "and I thought, 'What a great idea for a musical.' " Mr. Gilbert's "Assassins" was a narrative about a Vietnam veteran who becomes a Presidential assassin. Into it were woven readings from diaries, poems and newspaper accounts of real Presidential assassins.

"For example," Mr. Sondheim says, "there was a poem that Charles Guiteau wrote on the day of his execution, which began, 'I am going to the Lordy.' In fact, I quote two lines from it in one of my songs. That poem, and the letters and diaries, was what was most interesting about it. The narrative seemed to weigh the piece down, so we never did it. But I thought, 'I wish I had had that idea.' "

Years passed, and about two years ago, Mr. Weidman came to Mr. Sondheim with an idea for a musical about an American President. It reminded Mr. Sondheim of the old "Assassins" script, and he mentioned it to Mr. Weidman.

"My reaction to the title alone," Mr. Weidman says, "even before I knew what it was about, was that it was a great idea."

With the help of Theodore S. Chapin, who was Mr. Ostrow's assistant at the Musical Theater Lab and is now the executive director of the Rodgers and Hammerstein organization, they tracked down Mr. Gilbert and got his permission to, in Mr. Sondheim's words, "take his idea and run with it in our own way."

That involved investigating "the unexplored area between a narrative or book musical and a revue," he says.

"The idea that people from different eras would have scenes together was exciting," Mr. Sondheim says. "I loved the notion that John Wilkes Booth could talk with somebody who lived 50 years after he died. Once the barriers are down, you can allow yourself to cross eras and find parallels and contrasts."

At first, they thought their subject would be assassinations through the ages, but there was too much material, so they wound up focusing on American Presidential assassins. "The plan was that the piece would be built around character," he says, "around people who had something in common. They were entirely different people, but they were motivated by a similar kind of passion."

Some of them were politically motivated, Mr. Sondheim says, and some had personal motivations; "some were less than crazy, and some were more than crazy."

Mr. Zaks agrees. History, he says, "has tended to lump these people together and dismiss them all as just crazy." But it is more complicated than that. "What they did caused such upheaval, such terrible pain," he says, "that it seemed like they warranted a closer look."

Mr. Weidman says that the more he discovered about the assassins, the more his enthusiasm for the project grew. "They really are fascinating," he says. "Not just because of the dramatic and horrifying way in which they put punctuation marks at the end of their own lives and the lives of others, but because it turned out that the journey they had followed on the way to that moment was in each case extraordinary. When you put them together and looked at them as a group, they formed a kind of mosaic that had meaning and suggested that we really had something to write about.

"One of the things we found out as we looked at them is that we were not writing about shooting at the President of the United States," Mr. Weidman continues. "What's provocative and upsetting and disturbing is the lives they led up to that point and what those lives reveal. So in a sense the appalling and horrifying acts with which they ended their journeys were like tickets of admission into the show, rather than what the show was about."

When it comes to the meaning of the mosaic, however, or what the assassins' lives reveal, the three creators are more than a bit evasive.

"The piece should speak for itself," Mr. Sondheim says. "We don't want to tell people how or what they should think about it. We don't want to preach or promulgate."

And then the composer, who has presented his audiences with so many challenges over the years, gently issues another. "What would be nice is to tell them to take the journey with us," he says. "It's a real roller-coaster ride."