The Alexandria roller rink, a 32-year-old concrete hulk with grimy walls and wooden chairs worn smooth with use, has fallen on good times.

Only last summer, the aging Old Town landmark's doors were closed, its vintage Wurlitzer organ sold and its enormous maple skating floor silenced for want of customers.

"Business had fallen off," says an executive of America on Wheels, the East Coast chain that has leased the rink since it was built in 1948. "There weren't that many people who liked skating slowly to organ music. The organist had lost his following."

Now the old rink is echoing again with the constant roar of a new crowd of skating buffs as they whiz counterclockwise around the floor, oblvious of the rink's frayed interior.

"When I'm out there, it's heaven," said Johnny Artis, a 22-year-old cook, as he leaned against the railing taking a breather one night recently. "I can forget everything, get into my own style, just feel great."

Artis typifies the rink's new clientele, a more mature, middle-class crown than before, according to one of the rink's new managers, Marcus Ray, who with his partner, Sam Gilyard, 32, is responsible for the sharp turnabout in the rink's fortunes.

"Middle-class people would never come to a roller rink before -- they'd think it was anti-intellectual, one step below a bowling alley," Ray said.

That was before the roller disco fad swept the nation in the last two years, phenomenon that has boosted business at a number of area roller rinks and, at least for the present, staved off financial doom at the Alexandria arena.

Top 40 hits are blasted over eight 300-watt speakers fed by two 1,000-watt amplifiers in the cavernous skating palace, a far cry from the Wurlitzer days. Which is exactly the way the skaters like it.

"It's not like going to a disco where people ask you to dance because they want to pick you up," says Tina Ligerlis, 22, an accountant with an Annandale firm.

Ligelis, who says she hadn't skated for 14 years, since she used roller skates that "you tightened with a skate key" in her native New York, now skates once or twice a week, usually in Alexandria.

The $10,000 sound system -- virtually the only expense incurred in reopening the rink -- is manned by the rink's disc jockey, Joe Holliday, a 30-year-old mailman before the skates come out at night.

"What we've got to do now is bring in flashing disco lights, paint the place and generally spruce up the interior," says co-manager Gilyard. "It's a little dowdy."

Attendance, meanwhile, is healthy. Ray said about 300 people show up each week night, a number that swells to 500 on weekends and has hit 700 for special events. Admission is $1.50 to $3 per person, depending on the night.

The crowds area racially integrated, "one of the nice things" Ray said he has discovered since getting involved in the roller rink business in his off hours.

Ray, an MIT-educated civil engineer in the daytime, and Gilyard, who is a GS 9 computer programmer, were serious skaters who had never managed anything in their lives before they took on the Alexandria project.

After the rink closed last June, the two men went to New Jersey-based American on Wheels and made a bid to reopen it under their management. The firm's president, Marvin Facher, recognized times had changed.

"When I started out in this business in 1947, " Facher said in a recent interview, "the largest group of skaters were children under 12. For adults we had a very strict dress code. Men had to wear a coat and tie, women could wear dresses but not slacks." He gave Ray and Gilyard the go-ahead.

Ray then set out to visit more than two dozen places in the Washington area where people skate indoors and investigated the scene.

"I set a metronome to the music and discovered that for most frequently asked-for skating songs all had 121 beats to the minute," he said. "People also like to skate to any song with between 110 and 130 beats per minute. So those are the ones we use."

Ray plans to bring in live bands sometime in the future, and wants to install a $15,000 sound-sensitive light system that would be keyed to the music and pulstate to the beat.