TONIGHT, Washington bassist-singer Billy Hancock will rock the Wax Museum; early next week, he flies to France, where some hard-core fans know him as Rockabilly Hancock. His immaculate duck-tail coif, bright pink cowboy shirt, shiny leather jacket and insouciant attitude may define Hancock as a rockabilly artist, but he's quick to point out that what he plays is simply classic rock 'n' roll.

It's roots rock that many had forgotten about until a bunch of New Yorkers went to England and got people to sit up and listen to where so much of today's music came from. Following the success of the Stray Cats, musicians with "the look" have been thrown into the straitjacket of rockabilly. It's a distinctly American genre of music, but ironically, its greatest popularity has been overseas, especially in Europe.

For instance, Hancock has two albums out on a French label, with a third to be recorded live on tour this summer. His single "Rootie Tootie" went to No. 1 in the British rock 'n' roll charts without ever denting the American charts. He's toured France but hasn't yet made it to the West Coast. "Look at the Stray Cats," Hancock says. "Arista signed them worldwide for everywhere but here, said the music was not 'right' for America; they didn't think it would do anything. Now it's triple platinum. The Stray Cats are very good. But I think I did it first."

Hancock, a decidedly hefty fellow at 36, has been "in this business 20 years, 22 if you want to count the teen clubs." The raucous, direct energy of rockabilly, he insists, never disappeared. "It was strong in the '60s, weakest in the '70s; Credence Clearwater Revival had many hits with what I call rockabilly--'Looking Out My Back Door,' 'My Baby Left Me' and 'Bad Moon Rising.' The music never really died, but the style--the hair, the clothes that go with it, the image, the boutique part--just recently became alive again. The music's been here, but the people who sang it didn't look any different than other singers.

"My music really is just rock 'n' roll. It's no more rockabilly than NRBQ or Dave Edmunds, but if you do one rockabilly side on an album, you're a rockabilly band. And now if you have 'the look,' people will hear the music even if it isn't there. Everything the Stray Cats do isn't rockabilly, but some of the things Electric Light Orchestra does are."

Hancock's trip to France reflects the continental fascination with older American rock styles. He first went over in the summer of 1981 as part of the Bop and Roll Party, a dozen rockabilly performers touring as a package. He'll go back with his band, the Tennessee Rockets, this summer with added appearances in Luxembourg, Belgium and Finland.

According to Hancock, the French are bananas over rockabilly. "When I was over there before, we couldn't go into a little brasserie without some guy jamming the jukebox full of centimes and playing the Stray Cats over and over. And French audiences overreact: either they really love you or they really hate you. One act got bottled."

During 20 years, Hancock has not only played with just about every musician in Washington, but he's played every style of music imaginable. Not surprisingly, his musical roots are "real American." His mother worked in downtown five and dimes and as a pre-teen Hancock was exposed to what were then called "race records" from small labels like Appolo, Excello, Specialty, Imperial. "We had the usual supply of Perry Como and Eddie Fisher records, but in our household we also had Willie Dixon, Amos Milburn, Charles Brown, Floyd Dixon, Roy Milton." Hancock was also a fan of early country, what was then called "hillbilly music."

Hancock's love for small labels and roots music showed when he started his own company in the '70s; after lengthy negotiations, he purchased the right to use a classic rhythm and blues label's name, Alladin. Among the albums that came out were the first effort by the Nighthawks (about to be re-released by a New England label) and Powerhouse. "I haven't put anything out for a long time, but there is a lot of stuff in the can," Hancock says, including much material featuring super guitarist Danny Gatton; Danny and the Fat Boys (with Hancock and drummer Dave Elliott) were literally one of the heaviest Washington groups in the late '70s.

Over the years, there have been a number of bands: the Fat Boys, Swingshift (a mixture of rock oldies and western swing), the Manhattan Transfer-ish Radio City. Hancock also gave musical instruction, backed up the likes of Gene Vincent, Charlie Feathers and others. Now, he feels he's "just coming into my prime. I wasn't doing much in the '70s. I didn't have a niche but I was looking for it, I was uncovering everything. I knew I'd find it."