The salsa music blares from the stereo as four couples shimmy into a tight ring. "Sombrero!" calls out their leader, Gary Pennington, circling his hand above his head in the shape of a hat.

The men raise their partner's arms high and push the women into a fast spin. "Kentucky!" Pennington commands next, flapping his elbows like a chicken.

The dancers launch into an even more elaborate series of steps, twirling in and out of knotlike formations until each woman is facing the man next to the one she started with.

This is casino rueda, a Latin group-dance so thrilling and complex that the dancers have formed a troupe dedicated to teaching and performing it.

Based in Prince George's, the group has dubbed itself Salsa Linea, Spanish for "salsa line," because rather than simply performing casino rueda in its traditional closed-circle position, they have also devised ways of dancing it in a more audience-friendly line.

The troupe was founded about a year ago by Pennington, a physics graduate student who lives in Beltsville, and Barbara Bernstein, a former college math professor and Bowie resident. It meets most Saturday evenings for classes and rehearsals at the Eleanor Pernia Studio of Dance in Beltsville.

Membership is fluid, with several dozen men and women of varied backgrounds who might otherwise never have met taking part in the troupe's activities. Their ages range from mid-twenties to mid-fifties; their skills from beginner to advanced. The one thing they have in common: a love of latin dance.

"Our principal goal is the friendships that come from pulling it all together," Bernstein said. "You get to know many people at one time because you're dancing with the whole group. It's just a very social dance."

It's also a very challenging one.

Popularized during the 1950s in a Havana social club called El Casino Deportivo, casino rueda -- which means casino wheel or round -- uses the music and basic footwork of salsa. But it must be danced by at least two couples moving in synchrony, with frequent partner changes and dozens of intricate step combinations to choose from.

A leader calls out which one he wants the rest of the group to execute and also does its accompanying hand gesture in case the dancers can't hear him over the music. The result is something like square dancing, only much sexier.

The traditional combinations have Spanish names such as "Puente Complicado" -- complicated bridge -- or "Adios con la hermana" -- goodbye with the sister. Pennington and other members of the group have also invented new combinations of their own including not just the "Kentucky" -- named, of course, after the national fried chicken chain -- but also "Enchufla Al Gore," an under-arm half-turn done very stiffly.

There's even a step inspired by former President Bill Clinton's affair with Monica Lewinsky. ("Don't ask!" Bernstein said.)

Although casino rueda fell out of fashion in Cuba after the 1959 revolution, the Cuban exiles who flocked to Miami have kept it alive in clubs there.

But the dance is far less common in the Washington area. So it was that despite having spent years studying and teaching ballroom, folk and Latin dance, Bernstein had never heard of casino rueda until she happened upon a group of people dancing it at the Adams Morgan nightclub Havana Village several years ago.

She was blown away. "The steps are so beautiful and the partnership exchanges make it so lively," she said. "I had so much fun I could not sleep the whole night."

Bernstein started searching out other casino rueda aficionados, including Pennington, in area clubs and dance classes, and before long they realized they had enough people to form a troupe.

Since then Salsa Linea has performed in a variety of places, including various local Latin festivals and, most recently, the National Zoo's Fiesta Musical.

Often the group alternates its demonstrations of casino rueda with short lectures about the dance's origins and rules as well as its relationship to traditional salsa. The dancers then pull in members of the audience for a short, hands-on lesson.

Salsa Linea's next scheduled performance will be March 14 on the Kennedy Center's Millennium Stage. The program, which will run from 6 to 7 p.m., is free.

The group will also perform and teach a regular dance class at Joe's Movement Emporium in Mount Rainier on Jan. 25.

Although neither Pennington nor Bernstein are Hispanic, Salsa Linea has attracted a number of its members from the region's growing Latino population.

Jose Diez, 53, a structural engineer from Cuba who now lives in Silver Spring, said he was delighted to meet dancers from the troupe at a local nightclub this year. Casino rueda is the only type of salsa he knows so he was having difficulty adapting to the form of salsa that is common among Latin Americans here.

"I just can't dance with a woman from, say, Costa Rica, because she would expect me to do totally different moves," he said.

Diez, who is unmarried, added that not being able to dance can be a major social handicap for Latin American men. "You face terrible discrimination," he said, laughing. "You'll start to date a woman and then she'll find out you can't dance and say, 'Forget it!' "

Rita Ralph, 35, a health services auditor and mother of two who emigrated from Mexico, agreed, adding that she often used to wish her husband was a better dancer. "He likes to do it, but he can only do the basic steps," she said.

Then, a few months ago the couple, who live in Greenbelt, saw Salsa Linea perform at a festival.

"My husband said, 'you should go and dance with them,' " Ralph recalled.

Although she had never heard of casino rueda, Ralph has picked it up quickly.

"When we Latinos hear music we feel it in our heart and we can immediately dance to it," she explained.

At $6 a class, the lessons are a particularly affordable outlet for her passion to dance, Ralph added. They're good for her marriage too. "Now I can go out to clubs with my husband and not feel frustrated because I know I'll be dancing with Salsa Linea later."

But like other members of the troupe, Ralph said the best thing about the weekly sessions is the relief they offer from the stress of the week.

"It's a great distraction," she said. "I have so much fun when I'm here."

For more information about Salsa Linea go to www.geocities.com/SalsaLinea.

Salsa Linea group members performing the uncommon casino rueda style of group salsa dance at the National Zoo's Fiesta Musical in September.The synchronized moves in which members twirl and switch partners makes casino rueda resemble a Latin version of square dancing. "You get to know many people at one time, because you're dancing with the whole group. It's just a very social dance," said Barbara Bernstein, founder of Salsa Linea, whose performance caught the attention of zoo-goers, below, during Fiesta Musical. The troupe has developed its own way of performing casino rueda as a line dance instead of in the traditional circle.