'GLIMMER' WORTH THE WAIT.

Byline: Evan Henerson Theater Writer

John Spencer and Warren Leight have had this date for 10 years. Since Poughkeepsie. You might even say the two men understand the same music. And when the sound is jazz, that's an important connection.

The two men first became aware of each other during the New York Stage and Film summer festival at Poughkeepsie, N.Y., long before Spencer was the Emmy-nominated star of NBC's ``The West Wing'' and Leight the Tony Award-winning author of ``Side Man.''

``I think I knew him during a period of his life where he wasn't taking such good care of himself,'' says Leight whose newest play, ``Glimmer, Glimmer and Shine,'' opens tonight at the Mark Taper Forum. ``But I had seen his work since then, and it became obvious to me that he had channeled his demons into his work.''

Spencer is more blunt when he talks about his first interaction with Leight.

``When I first knew Warren, I was getting to know him through my own cloud of alcohol,'' says the 54-year-old actor, a recovering alcoholic who plays chief of staff Leo McGarry on ``The West Wing.'' ``My perception was positive, but maybe not as clear.''

These days, of course, the perception on both parts is positive. Spencer can act; Leight can write. Both men, as the jazz lingo goes, have ``chops,'' and Taper audiences will see how the collaboration plays.

Admittedly, we won't be the first. Spencer has hung on to the role of Martin Glimmer like a pit bull holds a freshly discarded steak bone. He originated the part at the premiere at the Williamstown Theatre Festival in 1999, a production which also featured ``Friends''' David Schwimmer, and again at the Penguin Repertory Theatre workshop in upstate New York. Spencer took up the role again during a workshop at the Long Wharf Theatre in New Haven, Conn., arriving via a red-eye flight on Good Friday.

Rehearsals for the Taper production dovetailed with a ``West Wing'' hiatus. Then, once President Bartlett's staff went back into action, Spencer spent his days filming and his nights rehearsing, an arrangement that occasionally meant 20-hour days. ``West Wing'' creator/executive producer Aaron Sorkin - himself a playwright - has been agreeable to the arrangement, and Leight figures he owes Sorkin a basket of flowers.

Not that Spencer would have given up the role.

``My theory is that Spencer will never let anybody else play this part,'' says Leight. ``He's been incredibly loyal and supportive.''

Covering the same landscape as ``Side Man,'' ``Glimmer, Glimmer and Shine'' follows two generations of a pair of musical families. There's Martin Glimmer, a dissolute trumpet player; his estranged twin brother, Danny; and Jordan Shine, the musician son of the Glimmer Brothers' former musical partner. Family secrets are unearthed and wounds reopened as Jordan begins a romance with Danny's daughter, Delia.

Spencer, who played the trumpet throughout his high school years, says his preparation for playing Martin Glimmer has meant ``living in a world of jazz,'' making friends of legendary horn men Dizzy Gillespie and Fats Navarro.

``I use a lot of music in work in terms of sense memories, getting in the mood and working on character,'' says Spencer. ``I'd be a very miserable person without music in my life.''

``Glimmer'' also deals with choices made by both the struggling artists and those who abandon their art for family considerations.

``I wanted to take a look at the guys who had gotten out vs. the guys who had stayed in,'' said the curly-haired and bespectacled Leight during a rehearsal break. ``Voyeuristically, I suppose I was interested in class in America.

``The original play was called 'Glimmer Brothers,' and I think the focus was more on the older generation. But there are two generations in this play,'' he added. ``This play is more about how the secrets that one generation keeps reverberate into the next. I guess there's a lot of secrets in my writing.''

And a lot of music. Spencer said his antenna starts going up whenever he encounters good writing. That intuition, he says, has led him back to series television - even after he was leery of returning to the tube after four years on ``L.A. Law.'' - and now to a play that sings.

``I'll look at the piece and see how I respond to what the piece is saying, and the character's humanity,'' says Spencer. ``There's good humanity, bad humanity and complicated humanity. If I respond to a character's humanness, that's usually where I'll find myself going.''

``Listen, ultimately how lucky am I as an actor who's 54 and has two of the great American writers writing words for him - Aaron Sorkin and Warren Leight?''

To hear him tell it, Leight's the one who's living large. With the Taper production, the playwright finds himself with a full rehearsal period, working with his cast and director (Evan Yionoulis) of choice. During his struggling years, (he wrote the 1996 comedy ``Dear God''), productions of his plays usually meant that Leight himself was painting the floor or supplying furniture from his own apartment. Leight, meanwhile, paid the bills by working as a journalist, a stand-up comedian and a screenwriter (he wrote the films ``Dear God'' with Greg Kinnear and ``The Night We Never Met'' with Matthew Broderick).

Then came the success of ``Side Man'' which, in addition to a successful Broadway run, attracted such stars as Christian Slater and Andrew McCarthy and netted Leight the Tony Award for Best Play in 1999. It will be the third most frequently produced play in the United States this season, with 14 scheduled productions including its L.A. premiere in May at the Pasadena Playhouse.

The success meant that Leight's days as a struggling playwright were over, and that his life would change in unexpected ways.

``If you wanted to, you don't have to spend an hour of your life writing,'' says Leight. ``You can just fill it up with symposiums and casting different versions of 'Side Man.' And then you have to make a living writing a movie or a sitcom.

``I think I lost control of my life for about a year and a half . It's strange going from nobody looking at anything you've done to people talking about you behind your back.''

The life of newly crowned Tony Award-winning playwright doesn't necessarily lend itself to creating new material from scratch. Fortunately, Leight says, he had the workings of a new play, which he had begun back when he was still struggling. ``Glimmer, Glimmer and Shine'' was partially inspired by the Penguin Repertory Theatre's rejection of ``Side Man'' because - with a cast of seven - it contained too many characters. So he began a new play with fewer characters. (``There's a real artistic impulse,'' he says dryly.)

``Now it's funny, because 'Side Man' gets done everywhere,'' says Leight, ``but an unknown writer with a seven-actor play is dooming himself to no productions.''

Leight had envisioned the Williamstown premiere of ``Glimmer Brothers'' to be more of a workshop, but a quick rehearsal period allowed for little exploration. He had more time for changes and development for the Penguin Rep version.

The Taper production, meanwhile, has given Leight the cast and director he wanted, a lengthy rehearsal process and all the frills a well-heeled regional theater like the Taper can afford.

``It's a sort of a ... backward process,'' Leight says. ``There was the finished production first, then the developmental production, then the workshop and now I think the play is ready to be seen.''

A New York run is likely, although Leight acknowledges he might have to wait for another ``West Wing'' window if he plans to keep his Uncle Martin of choice.

``You can't bring the play into New York without Spencer. I don't think that would be right,'' says Leight.

Then he laughs.

``Also, it would be stupid. It's not even, 'Oh I'm loyal to my actors.' It would be stupid. You won't get that performance twice in a row.''

``GLIMMER, GLIMMER AND SHINE''

Where: Mark Taper Forum, 135 N. Grand Ave. Los Angeles.

When: 8 p.m. Tuesday through Saturday, 7:30 p.m. Sunday, 2:30 p.m. Saturday and Sunday; through March 4.

Tickets: $30 to $44. Call [phone].

CAPTION(S):

3 photos

Photo: (1 -- cover -- color) John Spencer, left, and Jonathan Silverman in ``Glimmer, Glimmer and Shine''

(2) John Spencer and Alexa Fischer star in ``Glimmer, Glimmer and Shine,'' about the price a musician pays with drugs, booze and women.

(3) Author Warren Leight on the play's development: ``It's sort of a... backward process.''