An old dance for a new crowd. In growing numbers, young folks are waltzing their way to the ballroom, lured by good old-fashioned style and grace

UNDER two pairs of opulent chandeliers, in a room where the hand-carved mantels and gilt trim stop only for sets of French doors, about twenty couples are swirling in perfect sync to a waltz. Make that near-perfect sync. The setting is pure ``Sound of Music,'' but this isn't pre-war Vienna. It's 1987 Boston, and this particular Edwardian ballroom is just as likely to resound to a Rumba or a Cha Cha Cha as a waltz. The occasion is one of those evening ``adult education'' classes some people falsely associate with splattering clay pots, pompous poetry readings, and boggling home computer courses. Tonight's subject: Beginning Ballroom Dance, offered through the Boston Center for Adult Education (BCAE).

The Edwardian ballroom is the real thing - part of a turn-of-the-century Boston townhouse on elegant Commonwealth Ave. - even if the dancers are wearing their neckties at the after-work, half-mast position. The only standard is a pair of leather-soled shoes. ``Sneakers don't slide,'' explains one dancer, ``they squeak.''

That a great number of those wanting to learn ballroom dancing are normally sneaker-wearers points toward a relatively fresh discovery: Style and ``swing'' are mounting a comeback among the young.

``We don't keep any age statistics,'' says Charles Casanave, president of the Fred Astaire National Dance Association in Miami, ``but there is a definite trend in this country back to the more traditional ballroom dances by younger people.''

Mr. Casanave attributes the resurgence of swing to factors ranging from politics - ``dancing reflects broadly the conservative mood of the people'' - to sheer fatigue. ``You can only `disco' for so long,'' he says, ``and I think there's a tendency among young dancers to want to settle down to an easier way of expressing themselves.''

Others say disco, now largely gone and forgotten, actually contributed to the resurgence of interest in ballroom dancing.

``Disco dancing was the best thing that ever happened to ballroom,'' says Marge Melchionne, function manager at Moseley's on the Charles, a dancing-only club just outside Boston that boasts eight-piece bands several nights a week. ``When it [disco] faded out,'' she says, ``it left people thinking it was OK to dance in couples again. Now places like Arthur Murray Dance Studios are opening all over the place.''

Competetive ballroom dancing is particularly exhausting. During a recent re-broadcast of a national competition on PBS, co-host Juliet Prowse expounded on the sport's physical demands, as if the breathless post-dance interviews didn't say enough.

It's a long way from the shuffle-shuffle-twirl of Beginning Ballroom Dance to kicking up a flawless Argentine Flick in the manner of the stylish pros. But would-be dancers are undeterred.

``The Wall Street Journal reported about 15 years ago that the number of people enrolled in dance classes was greater than total enrollment in all US universities combined,'' says Ernie Garcia, a professional dance instructor from Providence, R.I., who says he learned under Fred Astaire himself. ``In between then and now there has no doubt been a big drop, but I think given the double flow now of older people with the young, it's probably about to be matched again.''

The BCAE concurs. ``Ballroom dancing, like most of our dance and exercise classes, are always the fastest to fill,'' says assistant director Jamie Jaffe, ``and it's significant that the people here are here not for college credits, but because of a genuine interest in learning to dance.'' Dance and exercise classes top enrollment for real estate and entreprenurial classes, cooking classes, and foreign language classes, all traditional favorites.

Some of the new-found interest springs simply from first exposure to an older way of celebrating. Ray Cheung, 29, and his 25-year-old fiancee, Cindy Wong, recall a Brown University commencement party last year. A pair of dance floors offered a juxtaposition of rock and ballroom dancing. ``The waltzing looked so much better,'' remarks Mr. Cheung, ``so graceful.''

When the two signed up for their BCAE class, they were a little surprised to find themselves in the mainstream in terms of age. Next June, at their wedding, they intend to show off what they've learned in Beginning Ballroom, and whatever they've refined in the more advanced classes they plan to take.

Mr. Cheung sees the growing interest in ballroom dance as part of `` a national trend back toward things that are classic, like good china and silverware.''

``A lot of couples just want to look graceful at their weddings,'' says Mr. Garcia. ``They're the ones who favor the elegant dances like the waltz.'' Swing, however, tops the list in overall popularity because it's so adaptable, he says. It also has some of the flash and speed that disco offered in the 1970s.

If one memorable occasion, like a wedding, isn't enough to justify hours of ``training,'' there are a growing number of other outlets for dancers.

``I found that clubs like the Kiwanas, Elks, and Sons of Italy have dancing a few nights a month,'' says Cheung, ``and they're usually open to the public at least part of the time.'' Specialized clubs like Moseley's are available in many places. .

``It's really a great thing for us,'' says Ms. Melchionne, ``because for a while it looked as if the art was ending with the older generations.''

``Kids start to learn,'' says Garcia, ``and their knowledge turns into real appreciation. It's very gratifying.''