"I REALLY want to keep doing the kind of music I'm doing, all the old music. I have a goal of learning a song a day, and that keeps me jumping," says Vicki Garno.

Garno, a 25-year-old singer of '20s, '30s and '40s jazz and swing standards, is playing with her trio--Swing Shift--weekdays in Ashby's at the Washington Hilton.

Ashby's, a spacious, mirrored lounge with a small dance floor in front of the bandstand, is packed many evenings with conventioneers--many of them the right age to remember the swing era. They come back night after night to hear Garno do tunes they danced to in their teens: "Don't Get Around Much Anymore," "Mean to Me" and "As Time Goes By."

The opening number of the last set on a recent evening was "This Can't Be Love," and the first notes had hardly sounded when a couple was locked cheek to cheek in a fox trot a few feet in front of the singer. Garno is appropriately vampish in dangling rhinestone earrings, a slinky fire engine dress with spaghetti-string straps and patent leather pumps with three-inch heels.

Garno became an old-movie fan in her early teens, watching Judy Garland and Lena Horne musicals. "Ever since I was about 13, I've been a jazz-era buff," she says. "I went to a yard sale and bought an album of 1920s songs and I just played that record all the time." After high school she got a job as a singing waitress in the District's Gaslight Club, where she sang Cole Porter, Gershwin and Ellington tunes with a Dixieland band. She has also sung with big bands in the area, and when the workload at Marymount College forced her to curtail professional singing activities for a spell, she sang in a church choir.

For Garno, the life of a performing artist is for keeps. "It's a lifelong thing for me," she says. "The more I do it, the happier I become." The young musicians who make up her regular working trio are no less serious.

Bassist Dave Jernigan has been a member of the house quartet for the Saturday and Sunday afternoon jam sessions at One Step Down for a year and a half. He volunteers several afternoons a week for rehearsal with a summer youth program, studies with a member of a symphony and takes a few students himself. "I've never worked full time in any other field except a short stint as a dishwasher," he says.

Swing Shift's Rick Harris is not only a full-time professional on the piano, which he has played, mostly by ear, since he was about 5. He also has given 10 years or so to the trumpet, and he is getting his lip in shape for a modern jazz combo he is putting together. The early inspiration to take up piano came from his father, who played a Fats Waller stride style at home. Harris says that, at 7 or 8, "if the tune wasn't too complicated, I could hear what he was doing and sit down and play it."

"I enjoy playing in this idiom as a study," says drummer John Zivard, who holds a degree in percussion from the University of Michigan. In addition to keeping time for Swing Shift, he teaches his instrument, plays in revues and show bands and is a member of a prominent area rock group, Root Boy Slim. Zivard insists that Swing Shift is "not doing a '40s act" and describes his coworkers as "contemporary musicians."

He once received a compliment from the late Ellington trumpeter Cat Anderson, who was a guest soloist with the college band in which Zivard played. "We played a few things as a quartet and he turned around and said, 'Oh, you're a be-bopper all right!' "