Tuxedoed musicians on an old-fashioned bandstand, stage lights playing on them softly, swing easily into "In the Mood," drawing a hundred or more couples out of their seats and onto the wooden dance floor of Glen Echo's old Spanish Ballroom. On Saturday nights in summer, big band music is back.

The dormant days of the Spanish Ballroom, tucked away in its sylvan setting next to the tiny settlement of Glen Echo, have disappeared with the return of summer weekend dances and festivals. The park, closed as an amusement center in the mid-1960s, is owned by the U.S. Park Service, which operates it as an arts center.

Amid the slightly faded splendor of the Moorish-style ballroom, with its brightly colored ceiling tiles, stuccoed walls, columns and arched windows, the Saturday-night dance crowd almost appears to have been transported from another era.

While the dress has changed since the 1930s and '40s, and baby boomers are now on the dance floor with people who lived through the heyday of big bands, the music and steps have stayed the same. The jitterbug, the fox trot and the polka are still the order of the evening and tunes such as "Chattanooga Choo-Choo" and "Dancing in the Dark" will bring a crowd of 300-plus to its feet in a hurry.

The Spanish Ballroom is perhaps the only place in the metropolitan area where big band music and ballroom dancing can be found on a regular basis, although they are offered on occasional evenings by a few Washington hotels.

Some might argue that ballroom dancing belongs to another time, but Richard Bray would disagree. Bray, who has organized the dances since they began in June 1983, said he has watched crowds of 30 to 40 people grow to an average of 350 dancers on Saturday evenings.

"In the Mood Again," the Spanish Ballroom theme for summer 1983 remains apropos, Bray said.

"The people are ready again. Little bit by little bit we have been growing, and once people come out and learn that it's nice and fun, they want to come back," he said.

While Bray said he expected the Saturday night dances to be popular, he didn't expect the increasing numbers of young people who attend regularly.

For 21-year-old Sherry Cipperly of Calverton, mastering the steps of the polka or the turkey trot isn't easy.

"I find it very challenging because it's something different. People don't normally do this but I like it," she said.

Last Saturday night was Cipperly's first visit to the ballroom, but she said she expects to be coming back, as does 23-year-old Dwan Vanderpool of Chicago. Vanderpool, who plans to move to this area next month, said she came "to have a good time and to do something different." The ballroom's sights and sounds allowed her to "step back into time," she said.

For Eleanor Jackson of Adelphi, Saturday nights at the ballroom bring back memories of visits to Glen Echo Park in the '30s.

"Things haven't changed, although I do miss all of the rides," she said. "But the ballroom -- it's as great as it used to be."

Music on a typical Saturday evening is varied, from waltzes to polkas, and the dancers range from enthusiastic novices to polished veterans.

It's not unusual to see one couple float across the floor with the grace of Astaire and Rogers and another bump and stumble and mumble, "Excuse me."

"It's a chance to watch people who really know how to dance, but you don't have to know how to dance to have a good time," said Robert Redmen of Rockville, who returned to the ballroom last Saturday for the first time in 20 years.

Loretta Kowalski of Daytona Beach, Fla., and Ted Sowinski of DuBois, Pa., said the sounds of the 17-piece BB Big Band spurred them to polish their steps as they prepared for competition in Florida later this month.

For the less experienced, an occasional intermission becomes the opportune time to work on that 1-2-3, 1-2-3 step.

Jan Levin, who has helped organize the dances, said that a main reason for the renewed popularity of ballroom dancing is that people want to get back to the "touch style of dancing." The response to the weekly dances has been "very positive," she said.

The Spanish Ballroom features big band sounds every Saturday night between 9 p.m. and midnight through October. Because the building is unheated, the dances are not held during the winter months, Bray said.

And as Saturday drew to a close, many couples lingered on the dance floor, looking as if they could dance all night