The lights came up on stage at the Gunston Arts Center two weeks ago and Beverly Geier began singing her heart out, as she has regularly for the last 35 years.

Geier belongs to the Sweet Adelines, a women's barbershop-style singing organization now in its 40th year. Currently a member of Potomac Harmony, one of four Sweet Adelines chapters in Northern Virginia, Geier has made a career of being an amateur singer, belonging to Sweet Adelines chapters across the country as her family has moved from one state to the next.

The organization has more than 250 members in Northern Virginia and more than 30,000 around the world. The international headquarters is in Tulsa.

On a recent Saturday night, more than 400 people turned out at the Gunston Arts Center in Arlington tospend a few hours listening to what Geier calls "an old American art form that we don't want to see disappear."

For now, anyway, that doesn't appear likely. Joyce Walker, president of Potomac Harmony, said that although the chapter is in a transient area, the group has always remained stable, never numbering fewer than 70 people.

On the world stage, however, the Sweet Adelines have seen a slight membership decline since the group's founding. Members attribute the loss to women today having less time for pursuits such as performances and rehearsals.

"When the organization started 40 years ago, the members were primarily homemakers," said Walker, who has been a member for 11 years. "Now, many people are working outside the home, so you do see an attrition in membership."

Geier, 59, joined her first chapter in Tucson in 1952 -- partly, she said, at the urging of her sister-in-law, but mostly because she was a frustrated singer.

"I grew up singing in school and in church choirs and I missed the outlet," said Geier, who said she sings bass.

As she moved around the country with her husband Bernard, who is with the Federal Aviation Administration, Geier found that belonging to the Sweet Adelines was like being in a sorority: There were groups wherever she went and it was an easy way to meet people.

In Fresno, Calif.; Billings, Mont., Milwaukee and Kansas City, "I could call up a Sweet Adelines representative and they would show me around, show me where the good schools were, where to shop and so on. Instant friendship."

The Geiers are a local version of the von Trapp family. Bernard Geier sang for many years with chapters of SPEBSQSA (Society for the Preservation and Encouragement of Barbershop Quartet Singing in America), and Beverly Geier has interested her four children in singing, though neither of her daughters is a Sweet Adeline -- yet.

"Each chapter has its own personality," Beverly Geier said. "If you compare Potomac Harmony to the interior of a home, I think you would call it Early American Country. It's very relaxed and friendly."

When she attended the international chorus competition in Hawaii earlier this month, Geier said, she realized that one of the benefits of membership is "meeting people from all over the world. Singing produces a harmony that is both mental and vocal."

However, it is not just the social aspects that have kept Geier with the Sweet Adelines for almost as long as the organization has existed.

"Basically it's the music, the singing. I like to improve my vocal ability . . . . Harmony barbershop-style produces a very tight chord structure, and I like close harmony."

So every Wednesday night, Geier attends rehearsal in the auditorium of the Gunston Arts Center. Like other Sweet Adelines, who practice in schools, homes and church basements, several times a year she puts on her costume and performs for aficionados and newcomers to barbershop harmony.

They won't be able to resist, either, when the program includes such old-time favorites as "How Can You Believe Me When I Said I Loved You When You Know I've Been a Liar All My Life?"