BRINGING A STAGE TO LIGHT
On the stage, a trio of white singers has just appropriated a black rhythm-and-blues group's song about the American dream of success and assimilation by releasing a sugary version of the ballad. As the black band and vocalists are overtaken by the pop group, the back of the stage fills with shadowy figures dealing cash to disk jockeys and the song changes to ''Steppin' to the Bad Side,'' the first all-out production number in ''Dreamgirls.''
It is a scene charged with motion that depends for much of its dramatic effect on the sharpened precision of Tharon Musser's lighting design. The upstage villains are bathed in ominous green light - the physical embodiment of the corrupt side of success - while the reality of payola literally dawns on the black musicians as brighter lights slowly rise on them.
Instead of a realistic set, Robin Wagner designed five mobile, spotlight-studded towers (reduced to four in the current production) that are constantly rearranged on the stage to suggest everything from the intimacy of a backstage reunion to a Las Vegas show palace, all with little more aid than a business desk or the drop of a beaded curtain. So the set, an integral part of the lighting design, also becomes a kind of ever-changing character in the show. Even the costumes by Theoni V. Aldredge take on added significance as, in ''Steppin' to the Bad Side,'' the now-wiser black performers triumph in patriotic red, white and blue. Working Closely Together
Mr. Bennett died on July 2, not knowing how well his reworked version of ''Dreamgirls'' would be received on Broadway. But his insistence on rethinking the show was no surprise to the design team that had been with him for more than a decade and a half.
''Talk about collaboration - I never knew the meaning of the word until I met Michael,'' Ms. Musser said during a recent conversation at the Greenwich Village town house where she lives and works. ''Lots of times, we didn't know whose idea was what. I've never known anybody who knew so well what lighting could do for or against him. Anything dramatic -lights, sets - he knew what it could do. With the 'Dreamgirls' tour, we had to come up with a design that could be put up in eight hours. I was very proud of it because it was a Michael production.''
Ms. Musser, who is 62 years old, well knows what constitutes a ''Michael production,'' having worked with him since 1971 when she designed the lighting for ''Follies,'' which Mr. Bennett co-directed with Hal Prince and choreographed. (All three won Tony awards for their work.) She has been a ubiquitous presence on Broadway since her first theater assignment, the premiere in 1956 of Eugene O'Neill's ''Long Day's Journey Into Night.'' Her work currently can be seen in the Neil Simon play ''Broadway Bound'' (she has lighted every Neil Simon show since ''The Prisoner of Second Avenue'' in 1971) and the musicals ''42d Street'' and Mr. Bennett's ''Chorus Line,'' as well as ''Dreamgirls.''
''I've never made any bones about the fact that I am about commercial theater,'' Ms. Musser said, punctuating her quiet responses to a visitor's questions with drags on an endless string of cigarettes. ''I work regional theater, I work dance - I came from the dance world - and like all that. But somewhere along the line you have to decide your priorities, and I am about commercial theater. Whether I would say that today, with the shape the commercial theater is in, I don't know. But I've been very lucky and came along at the exact right time.'' The Early Years
As she spoke about her introduction to the stage, Ms. Musser's eyes narrowed, drawing her face up in craggy relief. ''I was born in Virginia and went to college in Kentucky, which was where I really started getting into theater,'' she said. ''But I was fascinated with working on shows even in high school. I went to Berea College, a working school, which was great. Budgets for doing shows were nil, which was also great. I came out of there knowing theater, but I also knew that no way did I want to have anything to do with being on stage.
''Then I went on to Yale as a tech major, and I started thinking, Why am I getting a master of fine arts to pull ropes the rest of my life? Little by little I got into lighting there. After I came out of Yale, there was the design union to cope with. In the exam in those years, lighting was 10 points out of a hundred. Basically, designers did their own lights.
''So I worked at the 92d St. Y, which in those days was a real culture factory. We did three or four dance concerts a week, poetry readings, string quartets, children's shows, you name it. Two of us ran the stage, and we did everything. I stayed there a couple of years. A lot of the dancers were saying they didn't want to work without me ever. So I left and began freelancing in modern dance and did virtually every company around. Mainly the Limon company, but all the one-concert-a-year people. Doris Humphrey was my idol, because she was such a perfectionist.''
''Modern dancers are marvelous people,'' Ms. Musser said, pausing for a long pull on the cigarette. ''The thing is, there's no money in it. First Show Is O'Neill
''I finally got in the union after five years. The first show I did was 'Long Day's Journey,' with Fredric March, which was the luckiest first show you could have. Jose Quintero told the producers he wanted whoever did the lighting for Limon. Didn't even know my name. I was in New London, doing the summer dance festival. They asked me to read the script and I did. I thought it was long. And they asked me to come down to New York and I said, 'I can't, I'm in the middle of the dance festival.' They said, 'Well, can we come talk to you, and I said, 'Sure, if you're here from 12 to 1 in the afternoon, because that's my break.' When I think about that now, I think, 'How could you be so stupid?'
''And it opened, and it was a big hit and I thought, no wonder this is what I wanted to do. I didn't realize that was very rare, that people like Jose Quintero are very rare. Lighting, being a very intangible art, you need for a director to talk about atmospheres -especially with O'Neill, who was very specific about time of day, time of year.''
The following year, 1957, Ms. Musser joined the American Shakespeare Festival in Stratford, Conn., lighting shows there for 13 seasons. Throughout much of that period she worked with Jean Rosenthal, one of the seminal lighting designers for theater, dance and opera from the 1930's through the 1960's. Ms. Rosenthal was famous for illuminating a stage with broad washes of color. Ms. Musser went in a different direction.
''Jeanie and I had very different points of view about lighting,'' she said. ''I'm a leko person: I like sharp. And fresnels I find very little use for. She could talk for hours about the qualities of a fresnel. She loved to light air with fresnels, as she put it. I could dismiss them in a minute.''
Long before a show goes into rehearsal, Ms. Musser pores over sketches of the set, mapping the instrumentation (usually with the aid of assistants, who have included, over the years, such highly regarded proteges as Ken Billington and Jennifer Tipton) and plotting the cues. She still insists on focusing all of her lights once they are mounted - an arduous, time-consuming task - and thus spends as much time with a show during rehearsal as the director and actors. An Advance in Technology
If, along with the financial rewards, Broadway now offers greater possibilities to lighting designers, Ms. Musser can take much of the credit. With ''A Chorus Line,'' in 1975, she introduced the computerized lighting board to Broadway. The new technology permitted faster, more accurate lighting cues and greater nuance and allowed fewer people to operate more instruments.
At the moment, Ms. Musser is working on ''Teddy and Alice,'' which is scheduled to inaugurate the Tampa Bay Performing Arts Center later this month and, if all goes well, to come to Broadway in November.
In a conversation that ranged from the unmatched precision with which actors are placed in a Michael Bennett musical to the different qualities of light required by Mr. Simon's ''Plaza Suite,'' set in New York, and his ''California Suite,'' set in Los Angeles, the designer kept returning to one theme.
''I believe that if you pay people, you should see them,'' she said. ''It's how you see them that's my concern.''
Photo of Tharon Musser (NYT/Kim Garnick)