"Now," says composer Michael John LaChiusa to a handful of musicians and half a dozen actors in the windowless rehearsal room at the back of Signature Theatre. "I'm not sure how I want to get into this next number," he confesses, gazing at the score spread on the table in front of him.

A long hush ensues as everyone waits, much as the folks at Signature have waited nearly a decade for "The Highest Yellow," the long-planned new musical by LaChiusa and local playwright John Strand. It has been 10 years since Strand's "Otabenga" and LaChiusa's "First Lady Suite" were produced in the same season at Signature, followed -- no one remembers exactly when -- by Signature Artistic Director Eric Schaeffer's suggestion that the two of them collaborate on a musical about Vincent van Gogh. The show, directed by Schaeffer and featuring Marc Kudisch as van Gogh, Judy Kuhn as the painter's lover and Jason Danieley as his doctor, is in previews; it opens at last Nov. 8.

It's not that LaChiusa -- a "gay man, happily single," he says of himself -- and "the boys," as the 42-year-old composer calls his similarly aged collaborators, have been twiddling their thumbs. Strand has industriously cranked out work for Signature and Arena Stage; his new translation and adaptation of Alfred de Musset's "Lorenzaccio" will debut at the Shakespeare Theatre later this season. Schaeffer has kept Signature near the top of the D.C. heap while finding time to direct in London and New York and to oversee the ambitious Sondheim Celebration at the Kennedy Center a few seasons back.

LaChiusa, the most prolific composer in New York during the past 10 or so years, in 2000 had two large-scale, controversial musicals -- "Marie Christine" and "The Wild Party" -- on Broadway in the same season. Last summer, his "R shomon," a pair of related one-acts, debuted at the Williamstown Theatre Festival, with four-time Tony winner and "Marie Christine" star Audra McDonald anchoring a balanced ensemble.

Not surprisingly, it's LaChiusa who held things up on "The Highest Yellow." "I have to say, John and Eric were very patient with me," he offers contritely.

In the rehearsal room it almost seems as if he's out to make up for lost time, keeping the mood loose but setting a brisk tempo as he guides everyone through the rapidly changing show while Schaeffer dashes notes on Post-its. As one song winds down, the music surges on (the underscoring in the show is almost constant), and Danieley isn't sure how to time the dialogue. Danieley, playing Dr. Felix Rey as he treats van Gogh after the artist's famous ear-chopping incident, looks to LaChiusa, who is watching the page. Finally, Danieley ventures his line: "I want to see his room."

LaChiusa immediately corrects him. "Let the song end," he says. This is a lot of what these early rehearsals are about: making sure "some of the music doesn't step on the lines," LaChiusa explains a few days later. "Also listening to the actors, saying, 'Hmm -- if she's going to do it that way, I'm going to need this here. And if it's underscoring, what am I saying subtextually when I do this?' "

His pauses in rehearsal are rare, and as he makes decisions, pencils scribble all over the room. When musical director Jon Kalbfleisch asks LaChiusa to wait, LaChiusa doesn't understand.

"I'm writing the cues in," says Kalbfleisch from behind the piano.

"You have an assistant," LaChiusa replies, not being high-handed but eager to move on.

Kalbfleisch looks up and blinks. "She's keeping track of the script," he says of the woman furiously marking pages by his side.

After two zippy hours they come to the mandatory Equity break. LaChiusa declares that he's exhausted and heads to the auto-laden alley -- car repair shops surround Signature -- for a smoke.

Laurence Anholt's "Camille and the Sunflowers," a kids' book, put the idea of a van Gogh musical (for grown-ups) in Schaeffer's head. Recalls Strand, "My first reaction was, 'How would this not be "Sunday in the Park With Vincent"?' Eric said, 'That's for you to figure out.' "

The solution was to make the story not about van Gogh but about the doctor who treats him -- "about Vincent's effect on the doctor," says Strand, "and his effect on us."

LaChiusa says: "I think Vincent was the one who really made us modern. He had such an amazing presence on this planet in such a small amount of time. Yet what he did was . . . he broke it all down. He came along at the right time, although he would not say he did because he only sold two paintings in his lifetime and everybody, you know, hated his work so majorly."

Once everyone signed onto the idea, Strand created a first act and sent it to LaChiusa. "I thought it was really quite spectacular," LaChiusa says. "A lot of places for music in it." Two weeks later, he had a score for the act.

That much of "The Highest Yellow" was given a public reading that seemed to please everyone, and then the project hit a wall. Strand kept writing second acts, and LaChiusa kept shaking his head. (The give-and-take of the process sounds a lot like the librettist giving and the composer-lyricist taking: According to Strand, who was getting his first real introduction into the world of musical theater, LaChiusa asked for monologues where songs would go, material not intended for final viewing. Then LaChiusa "would cannibalize the monologue for the lyric," Strand says evenly. "That was interesting.") "I was upset with myself about it," LaChiusa recalls of his indifference to Strand's second-act drafts and his need for less polished material. "It was a good play, and yet sometimes a good play -- I want vomit sometimes, you know what I mean? I want stretches. . . . I told the boys, 'You know, maybe it's a play. Go do it as a play, because I can't find my way into the second act.' "

And then Michael John LaChiusa got very, very busy.

He had been in New York since the early 1980s, sporting a Mohawk haircut as punk petered out; he says there is a picture of him somewhere accepting a grant and smiling from beneath that Mohawk next to Stephen Sondheim. He supported himself through music directing and accompanist gigs, wrote songs, tried to get them sung on the cabaret circuit. "The regular route that one took in New York in the early 1980s," he says, "was still to play the piano bars, play the off-off Broadway shows, try to get your name around."

LaChiusa eventually joined the BMI workshop and met a set of mentors who "looked after me and kept me in line and made me try to really be the best I could be as a lyricist and composer for the theater. I didn't want to do anything else after that." These days he passes the lessons on as an adjunct professor at New York University and depicts himself as pretty strict: "Girl/world -- that doesn't make it in my book," he says with disdain. "You can make a million dollars with that rhyme if you want, I don't care. But in that classroom, you show up with a rhyme like that, you are so on my [rhymes with 'hit'] list."

He cranked out camp stuff that now seems out of character for a man who has been held up as the poster boy for Difficult Musicals. He got noticed at a BMI showcase; he created more serious material. By the early 1990s, the pooh-bahs at Lincoln Center and the Public Theater were interested. In his inaugural year as the Public's producer, George C. Wolfe presented "First Lady Suite," LaChiusa's imaginative take on the hidden lives of Mamie Eisenhower, Jacqueline Kennedy and other presidential wives.

In 1994 Lincoln Center staged his "Hello, Again," inspired by Ar- thur Schnitzler's ever-popular "La Ronde." Hal Prince directed LaChiusa's "The Petrified Prince" at the Public, and in 1996 LaChiusa earned a Tony nomination for his book, with Graciela Daniele and Jim Davis, to "Chronicle of a Death Foretold."

LaChiusa began to emerge near the head of a small new core of challenging, hard-to-categorize young composers -- "The cluster that got press," he calls the group, which is usually identified as Adam Guettel ("Floyd Collins"), Jason Robert Brown ("Parade"), Ricky Ian Gordon ("My Life With Albertine") and Jeanine Tesori ("Caroline, or Change").

So it was not out of nowhere that LaChiusa got his double-barrel break on Broadway, backed by two of the most respected theaters in New York. "Marie Christine" came first, produced by Lincoln Center; LaChiusa relocated the Medea myth to 19th-century Louisiana. The show was massive and extremely grim, and it sparked controversy not just because it bucked the always-strong tide of sunny tradition in musicals but because the score was so demanding that even the formidable and classically trained McDonald could sing it only six times a week, rather than the standard eight.

" 'Marie Christine' in my mind should have been performed for three performances," LaChiusa says now. "Three. Only three. It's huge, and it's intensely difficult. . . . There was no way, shape or form that one could have ever done eight performances a week of that."

Amazingly, "The Wild Party" -- the second Broadway musical that season to be based on Joseph Moncure March's poem of Jazz Age decadence -- kicked up a bigger fuss. Wolfe wrote the book with LaChiusa, directed and rolled the dice in guiding the show uptown to Broadway. LaChiusa's seamy jazz score provided showcase moments for plenty of performers: Eartha Kitt, Toni Collette, Mandy Patinkin, Tonya Pinkins and Kudisch. As with "Marie Christine," the density and dark vision failed to win over critics or audiences, and the tide of red ink led to heavy-duty scrutiny of the Public.

"The attack on George was so ruthless and so unnecessary," LaChiusa says. But on another level, he claims, he enjoyed the hullabaloo: "No one shrugged, which they do at most of the Broadway shows I go see."

And the lessons? "You can't control anything. There's no way. You can't control the press, you can't control people's reactions. You just have to work really, really hard."

"The victory," says Wolfe, "is that he's still writing, and the output is still there."

After "Marie Christine" and "The Wild Party," LaChiusa went to Chicago, where he wrote an opera called "Lovers and Friends (Chautauqua Variations)," then to Tokyo, where he wrote an adaptation of "The Nutcracker," and then into a funk.

"I was very upset with the reception of 'Little Fish,' " LaChiusa says of the off-Broadway musical he did last year about a woman trying to quit smoking. "It was a really fun score for Second Stage. And, I don't know. I went through something. It wasn't a, a, breakdown or anything like that. It wasn't that severe, healthwise. But I went, 'My God, they don't want the hard stuff and more challenging material here in this city from me. They don't want something nice and fun, either. What am I supposed to do?' " He pulled out "The Highest Yellow," rearranged things, roughed it in -- "just this mess," he says. "And I mailed it back to John and said, 'There. Make something of it.' And he did." A few weeks later, a second-act score was born.

"So, yeah, time went by, but it was two weeks here, two weeks there -- it took about a month to write the [expletive]," he laughs.

"When he gets it in his system, it really pours out," says Schaeffer.

"I always like to think you could write a musical in a month, really, if it's any good," LaChiusa contends. "But sometimes five years can intervene. I had to be ready to deal with it."

By his own account, he "lived well" during "Wild Party" and "Marie Christine" -- "I knew it was never going to get as good as that," he says -- and then he volunteers that 9/11 hit him hard. "I don't want to use that as an excuse for anything, but I think it did something in my head, being there, being part of that." And obliquely, it brought him into "The Highest Yellow." "The angst and the depression I felt afterwards, the deep, psychotic almost, grief that I -- that any of us felt. Finding myself in a place that was desolate."

His recent shows are modestly scaled, but the two he's offering this year, at least, display tremendous emotional scale -- real cataclysm in the music as characters reach shattering crises, but with sublime beauty in each piece as well. Says Wolfe, "He requires incredible levels of musicianship from actors, and dramatic ability from actors, because his songs are not just pretty moments -- they're deeply embedded in character and in story."

"No More" is the climax of the first act in "R shomon," a searing number in which the character sung by McDonald wishes her husband were dead. The force of it -- the layered, complicated composition, the emotional and technically formidable performance -- pinned the Williamstown, Mass., audience's ears back. As the lights came up at intermission, one woman, duly impressed with the way LaChiusa's material seemed tailored for McDonald's gifts, used a baseball analogy: "If I were a solo singer, I'd love someone who wrote in my wheelhouse."

For "The Highest Yellow," LaChiusa says he is using "a soupcon of French music of that period that Rey would probably have heard in one of his mother's salons, or at least his fantasy of what Paris music would have been like." He adds that he has taken liberties, made it modern -- "what Vincent saw. What was going to happen. . . . Some portions of it are atonal. There are some sections where I've experimented a lot musically."

He has also drawn from the paintings. "The Highest Yellow" may be the doctor's story, but it takes its tone from van Gogh -- the thick shimmer of light, the swirl of ungovernable passions. "Just harsh and violent and bloody when it needed to be," LaChiusa says of the painter's art, "and the colors are so brilliant. And when you explore what made those colors so brilliant, you realize that there's something very dark next to it. . . . Also, he used his whole hand, his whole body in the painting, so there's density, actually, in the music that I wanted to play around with. . . . It was fascinating trying to figure out what would be the aural equivalent of the colors that he used."

"You need the dark to make the light / Lighter," sings the mistress, and even after the show is over, that unpretentious line lingers like a light-fingered article of faith.

Michael John LaChiusa's "The Highest Yellow," about Vincent van Gogh, is at Signature Theatre."You can't control people's reactions. You just have to work really, really hard," says Michael John LaChiusa. Below, from left, Stephen Gregory Smith, Donna Migliaccio, Marc Kudisch and R. Scott Thompson in "The Highest Yellow."