When the Widespread Depression Orchestra first performed in Washington a year ago, no one knew quite what to expect.With a name like that, they just had to be another rock group.

Not so: They are a scaled-down big band of nine musicians in their 20s who recreate the music of Ellington, Basie, Jimmie Lunceford, Cab Calloway and other great swing bands of the 1930s -- hence the name. They open this eveing for a two-nighter at the Cellar Door.

How did it come about that these youngsters, growing up in the rock years, turned to big-band swing? Here is how three of them explain that anomaly.

Jonny Holtzman, leader, vibes/vocal: "I grew up in the Bronx at the tail end of '50s greaser music. The first time I got involved in music was in high school when I played banjo in a jug band. In college I was in a rock group with saxes that concentrated on R&B. We started getting exposed to big-band swing of the '30s and '40s through a record here and there and I thought: If I like it and I'm this young, then other people my age could like it, too."

Michael LeDonne, piano: "My father was a jazz musician, a guitarist, so I was kind of spawned on the stuff. He listened to a lot of Armstrong and Charlie Christian and got me hip to Art Tatum very early in my career."

Michael Hashim, alto-saxophone: "I was about 12 and my mother, who was musically inclined, urged me to take up an instrument. Just by a process of elimination I arrived at getting an alto saxophone. And since I had no recordings of any kind, I went to the supermarket and bought some 39-cent records. One of those I bought, because it had a saxophone on the cover, was a Johnny Hodges album."

The next step should have resulted in the Widespread Depression Orchestra coming together and soon swinging like Basie. But it didn't. At first, it was a band without a fixed identity.

"It happened over the last eight years," Holtzman explains. "We never decided we were going to play big-band swing. We heard something we really liked and we put it in the book. When the guitar players left, we replaced them with horn players. There are 13 people who have been in and out of this band, so a lot of evolution took place."

Holtzman believes that swing is the music of the future, that it will "dominate the pop scene once again -- in the '80s." One of his goals as manager of the orchestra, he says, "is to show that young people are ready to listen to good music with a lot of beat and soul to it." His ultimate objective is to demonstrate that circumstance to the record companies so that they will "quit putting out all this disco crap."

The Widespread Depression Orchestra is not a replica but a smaller version of the original big-band units, with trumpet, trombone, three-piece reec section , four rhythm players, vibes, piano, string bass and drums. "We don't go about it with an attitude of, 'Hey, remember this one?' -- and then play the solo, for nostalgia's sake, like the guy played it back then," Holtzman says. "We go about it like we were one of the bands in the '30s and '40s. We're developing our own soloists and our own style."

But the musical interests and vocabularies of several members of the orchestra are not confined within the big-band idiom. Among LeDonne's principal influences, along with Tatum and Hines, are the two foremost exponents of bop piano, Bud Powell and Thelonious Monk. Michael Hashim confesses to a passion for early Ornette Coleman and the outrageous, to some, saxophonic wailings of the late Albert Ayler.

But if they decide to follow such proclivities, it is not likely they'll find that the Widespread Depression Orchestra still has a place for them. As Holtzman says, "It don't mean a thing if it ain't got that swing."