LONETTE McKee's first experience with the white lights of Broadway was not a pleasant one. She spent four weeks rehearsing the lead in a musical, then was fired and replaced without explanation, right before the show was to open. (and close.)

"I thought, if this is theater, I don't want to do it," she said, her big black eyes glowing like coals at the mere recollection. But life, as she will tell you, has a strange way of arranging itself for the best, and there she was last week in a dressing room at the Kennedy Center with the elaborate Victorian costumes of Julie in "Show Boat" hanging on a rack behind her.

She has played the part since last June's opening in Houston, on the road for all but two months of that time. (The show closed for two months when star-billed Donald O'Connor developed complications after an appendectomy.) McKee took advantage of the hiatus to marry a man she met during the San Francisco run; he was the doorman at the Orpheum Theater, who works as a youth counselor during the day.

McKee, whose cream-colored skin, dark hair and fine features would allow her to play anything from an Italian to an Israeli, is the first black woman to play the part of the secretly mixed-blood Julie in a major American stage production. (Lena Horne played it in a truncated re-creation in the movie "Till the Clouds Roll By," a biography of composer Jerome Kern.)See MCKEE, K5, Col. 3 Lonette McKee; by Harry Naltchayan Lonette McKee MCKEE, From K1

The part is one of those small but pivotal roles that are always sought after. McKee has two classic songs, "Can't Help Lovin' Dat Man" and "Bill," which she delivers in a rich, intense contralto that demands attention. Julie is married to Steve, a white man, and when it is revealed that she is part black, they are ordered out of town; miscegenation was illegal.

Helen Morgan, then a 27-year-old singer famous for her melancholy songs (and a fondness for brandy), was the original Julie in "Show Boat" when it opened in 1927. It was immediately hailed as a masterpiece, precedent-setting because it had both music and a serious story. The show ran 575 performances before producer Florenz Ziegfeld closed it, but he reopened it in 1932.

Although the cast includes a vast chorus of slaves, the only black actor in a major role in the first production was Jules Bledsoe, who played the part of Joe made famous by Paul Robeson in the 1932 revival. Even the part of Queenie, the cook, was played by an Italian, Tess Gardella, who had a blackface act as "Aunt Jemima" before she joined "Show Boat," and that's the way she was listed in the program. (A black actress, Angeline Lawson, replaced Gardella in the national tour of the 1932 revival.)

The first line of the opening chorus of the show illustrates, in a way, how changing attitudes about racism are reflected in the theater. In the first production it went, "Niggers all work on the Mississippi . . ." In the 1936 film it became "Darkies all work . . .," in the 1946 Broadway revival they were "Colored folks," in 'Till the Clouds Roll By" it went "Here we all work . . .", and in the 1966 Lincoln Center revival the chorus was cut entirely. In this production, which is scheduled to open on Broadway next month, it's back to "Colored folks."

McKee finds fault with the argument that black actors should not perform in a show that portrays slavery and prejudice in benevolent terms, a plaint she has heard from several friends.

"We have to work, we have to make money," she said intently. "We have to achieve success--it's only then that we can turn around and hire other black people! At least we're working. You have ignorant people everywhere--people who will come to see this show and think, 'Look at those mammies--they can really dance.' But anyone who has any sensitivity will say, 'That's the way we treated black people, we really did that.' "

She grew up in an integrated neighborhood in Detroit--at least it stayed integrated until 10 or 15 years ago, she said, when all the whites moved out. She is the child of "a father who is very black, and a mother who is very white," and while her integrated neighborhood and parochial school allowed her to grow up without too much harassment, the arm's-length attitude of most members in her parents' respective families made it clear that she was different. Her parents are now separated, and she is estranged from her father.

McKee dropped out of school in ninth grade--but not for the usual reasons. At 14, she had a hit record in Detroit: "Stop, Don't Worry About It," and the nuns were not very understanding. "It was impossible to pursue my career," she said. For two years she played clubs with names like the Metropole and the Rooster Tail, with her mother as chaperone and manager, learning show business the hard way.

"We were ripped off a lot," she said. "Like we didn't know you should always get paid right after the show, or that when you do a promotional appearance for a record somebody's making money and you should, too. We thought you did those just to be nice. So we got bitter, and I decided to quit when I was 16."

Her older sister was a showgirl, and McKee went to live with her in Los Angeles. She spent the last years of the '60s "running on the beach and writing music," until she got back in touch with the producers of her first record, and they signed her to do an album. "It was not a hit."

Being "real skinny and real young," she turned to modeling, but the demand for exotic mannequins was not yet in flower, and she was not getting any jobs. "You had to be one or the other, and I didn't look black enough or white enough," she said. But the work led to a casting call for a movie called "Sparkle," the story of three sisters who, Supremes-fashion, become a hit recording act. Although she got raves for her performance, the movie disappeared quickly.

Once again, she dropped out for a while, turning down the Cleopatra Jones-type parts that she was offered and taking acting, singing and dance classes instead. "My own naivete' prevented me from going ahead at the time," she said. "I wasn't prepared for the film world coming at me like that. I didn't know what to do."

She did two more films, "Which Way Is Up," with Richard Pryor, and "Cuba," with Sean Connery, and then after her first chastening experience with the theater, she finally made her Broadway debut last season, in a musical about the baseball player Jackie Robinson, "The First," which closed five nights after it opened. She has also recorded an album of her own music for Warner Bros., "Words and Music."

She has learned to adjust to the rigors of the road, finding the "Y" in each town for her five-mile daily jog and workout. She said the "vibrations" in Washington are good, "calm and peaceful," as opposed to Denver, where the vibrations were "dark and uncomfortable." But she hopes the show will be a hit in New York, and that she and her husband can settle down for a while.

"My agent said my forte was the stage," said the woman who grew up knowing Broadway only as something she heard about on "The Ed Sullivan Show." "I think she's right."