WHEN LEAD singer Jerry Lawson and the rest of the Persuasions appeared on "Do It A Cappella," the PBS special directed by Spike Lee last year, Lawson saw it as the ultimate vindication of his whole career. As he looked around the soundstage, Lawson saw examples of the worldwide resurgence in unaccompanied singing: South Africa's Ladysmith Black Mambazo, England's Mint Juleps, New Jersey's Rockapella and the Grammy-winning Take 6.

"It was such a wonderful feeling for the Persuasions," Lawson recalls, "because it proved we had accomplished something; it showed we weren't one of these groups that just put out a few records and disappear. When we started out 28 years ago, a cappella barely existed, but we kept it alive and now a cappella is happening all over the world. It's like working on a car for 28 years, and when you're finally finished, people see it and go, 'Wow!' "

The Persuasions, who perform at the Birchmere Saturday, shared a dressing room during the TV special with Take 6, the Alabama a cappella gospel sextet whose shows now sell out.

"Their success makes me feel wonderful," Lawson proclaims in the same husky, booming voice he uses on stage. "There's always room for others. I'm 47 years old and the guys in Take 6 are kids; they're going to carry it on. When they told us in the dressing room how they listened to the Persuasions all through college or when they praised us on TV on 'Good Morning America,' it makes me feel like there was a purpose to the Persuasions. I feel like we've opened the door for someone else."

The Mint Juleps, an all-female sextet from England, were especially excited to meet the Persuasions at last. It seems that the women had never heard of a cappella singing until a few guys they knew tried to impress the women with some street-corner harmonies.

"They asked the boys, 'What's that?'," Lawson relates. "The guys said they learned it at a workshop led by the Persuasions in London about 15 years ago, and that got the Mint Juleps interested in a cappella singing. Like they say, 'Everything that goes around comes around.' "

Lawson was particularly impressed with Ladysmith Black Mambazo, the stars of Paul Simon's "Graceland" album and tour.

"I had to sit down and really listen hard to Mambazo," Lawson says, "because that's our roots. When we started singing a cappella on the street corners, we had no idea it reached all the way back to Africa. We were singing it for self-enjoyment, but for them it's a way of life -- it's their national anthem and their prayers. They showed us a whole other side of a cappella."

The "Do It A Cappella" TV special and the subsequent soundtrack album on Elektra (featuring three Persuasions tracks) have provided a new lift to the group's career. The special was broadcast all over the world, and the Persuasions' agent has been getting calls from the most unlikely places. The least likely of all was Vietnam. It seems that a lot of U.S. soldiers had tapes of the Persuasions' 1972 "Street Corner Symphony" album and many Vietnamese still listen to it. Lawson hopes that Vietnam will be included on the group's upcoming Far East tour.

In conjunction with the TV special soundtrack, Elektra Records also rereleased the Persuasions' 1977 album, "Chirpin'," which Lawson calls his favorite second only to "Street Corner Symphony."

"It's been nine years since we've had any album at all under our own names, but we just started work on a new one last week," Lawson says. "Ichiban Records should have it out by the time we come back to D.C. to play Anton's in May."

When the Persuasions were at Anton's last July, they asked D.C.'s Finest, an a cappella quintet of three active-duty D.C. police officers and two retirees, to open each show. It's been common practice for the Persuasions to befriend the local a cappella group that opens the show in nearly every city they play regularly. Often the friendship extends to dinners in private homes -- a personal touch that makes touring much more bearable. Last summer in Washington, Lawson lost a dental plate, but the officers in D.C.'s Finest wouldn't rest until they had safely delivered him to a dentist.

It's stories like that provide Lawson with satisfaction after a long and sometimes difficult career.

"Oh, there were lean times," he admits, "but we never had to take day jobs and we never thought about quitting. There was a time when the family tree of a cappella singing was only a single stem, and that was the Persuasions. But look at that tree now: It has lots of branches and all the flowers are blooming."

THE PERSUASIONS -- Appearing Saturday at the Birchmere. Call 703/549-5919.