On Saturday night, Mr. Henry's Connecticut Avenue was transformed from a nightclub to an oldtime church for a few hours. In her last Washington performance, at least for a while, Julia McGirt and her backup musicians had the capacity crowd of 125 clapping and stomping to the gospel standard "Goin' Up Yonder."

On Monday, McGirt left for New York to become an understudy for the role made famous by Jennifer Holliday in the Broadway hit "Dreamgirls."

The contract she signed this week was a dream long in the making for the Rowland, N.C., native. McGirt has been belting out contemporary, jazz, gospel and rhythm and blues tunes in Washington nightclubs for five years, accompanied by pianist David Ylvisaker, whom she met when they were students at the North Carolina School of the Arts.

She auditioned for Dreamgirls last October when the show's producer, Michael Bennett, conducted a talent search here. But too many near misses had made McGirt a skeptic, and she rejected an offer to join the company seven times--before she even saw the show.

McGirt had spent a grueling year in New York after her North Carolina training as a classical singer, supporting herself with waitress jobs and in a factory where she pasted swatches of fabric in department store catologs and auditioning for one Broadway show after another.

"It was always, 'You're good, but . . . ,' and I think that's what motivated me because I got tired of people saying I was good, but," she recalled of that period.

She auditioned for the movie "Hair" in 1977 and made it through the first cut. In all, she was called back 12 times. "I just knew I had the part," she said, but eventually she was told, " 'We only need four girls, and you're the fifth.' "

That rejection sent her back to Washington where she had worked with the D.C. Black Repertory Dance Company, an arm of Workshops for Careers in the Arts. Almost immediately she left for Boston where she and Ylvisaker worked in a club that paid $35 a night, she said. "I was singing 35 songs. My throat was so sore, and . . . we were so thrilled to have this job." Realizing eventually "that we were being had," the pair decided to make their fortunes in Washington.

An initial gig at the Top o' the Foolery led to a series of club dates, many in spots that no longer exist: Pigfoot, Manuel's, Harold's Rogue & Jar, the Cellar Door and W.H. Bone's. The unlikely duo--a black woman from North Carolina and a white man from Cambridge, Mass.--also worked hotel and motel lounges.

"When I started doing my nightclub act, the theater people I knew were saying, 'Oh, you pitiful child.' I guess they thought I would be a lounge lizard all my life. But there are different ways to get what you want," McGirt said in a recent interview. She found there were lessons to be learned in nightclubs.

"I'm very shy, really inhibited around people. So for me to get on stage and do what I do really baffles me," she said. ". . . I don't like being on stage and I don't like crowds and here I am in the business that requires both of those things. It used to make me literally sick. But I worked around it."

"Relax. There's plenty more to come," she admonished the weekend crowd at Mr. Henry's after singing a "Walk on By" reminiscent of Dionne Warwick. Her soulful version of the ballad "Sometimes When We Touch" moved some couples to hold hands. Then she shook them up with the high-energy funk tune "Turn Your Love Around."

"If you give the people what they want, there's no way you'll ever have to worry about food or a roof over your head," McGirt said. "I found that when I started having fun on stage the audience started having fun, too."

At the "Dreamgirls" audition she sang Patti LaBelle's "Music Is My Life," then, nervously tapping a tambourine, sang "Bring Back Springtime," an original composition for which she wrote the lyrics and Ylvisaker wrote the music.

"When Cleavant Derricks a cast member who was handling the auditions waved at me I thought he was saying, 'That's enough, thank you.' But then he said, 'Could you start over . . . this time without the tambourine.' . . .

"When they called me back I started having flashbacks of 'Hair' and thought, 'They're going to have me keep coming back.' I got there late, wearing my sweats, and they were doing a movement routine . . . . I said, 'Lord, please guide my feet because I don't know the first thing about what I'm doing.' I got through the movement okay and then I sang 'God Bless The Child.'

"That worked. That worked."

Although Bennett said he wanted her for "Dreamgirls," weeks went by with no further word--to her embarrassment, McGirt said. "I thought people would think I was making up a lot of things about 'Dreamgirls.' "

Eventually an offer came to be second understudy for Jennifer Holliday in the Los Angeles show. She rejected that offer and a subsequent one to become understudy for the part of Effie White the Jennifer Holliday role in New York.

"They called seven times, and each time they offered more money. . . . I told them I've worked with David for 10 years and I couldn't just give that up for 'Dreamgirls.' "

When McGirt finally went to see the show, she said, "I was sick about having turned it down. I said, 'I have to do it.' "

McGirt is only taking a leave of absence from Mr. Henry's. "I just felt like if it doesn't work out I can always come back to something that I know is here."

Her mother, a day-care instructor, and father, a plumber, are proudest of the time she sang in a gospel extravaganza at the White House during the Carter administration, and they are excited about "Dreamgirls."

For McGirt, however, it's a dream that has not quite yet come true. "I'm still pinching myself and I'm not really sure I'm awake," she said. "I'm not getting excited until I'm there and on that stage and really doing it."