The Texas Tornados play what the Fab Four would have if they had gone Tex Mex. Pop salsa. The kind of music you should hear on a Philco AM radio in a '60-something Ford cruising along the Rio Grande.

Maybe because the four fiftyish musicians have been making songs-to-smooch-to longer than Ford's been making Mustangs. And they do have a touch of Liverpool in them. Guitarist Doug Sahm and accordion player Augie Meyers outsmarted American audiences during the British Invasion by coming up with an English-sounding group, the Sir Douglas Quintet, and scored in '65 with "She's About a Mover."

The dash of romance comes from country crooner Freddy Fender, who made girls swoon in the '70s with "Before the Next Teardrop Falls" and "Wasted Days and Wasted Nights." Flaco Jimenez adds the swing with rollicking accordion polka chords that he learned from his papa, Santiago, who used to play at German and Czechoslovak weddings in San Antonio.

Add the random switches mid-song from English to Spanish and you've got what some critics call a Tex Mex Traveling Wilburys or a Mexican Beatles: lots of harmony, lots of blues and lots of fun.

"One critic said we were too authentic," says the boisterous Sahm, laughing. "How do you get to be too authentic?!"

All four musicians are old pals. Sahm was 17 the first time he played with Fender, on the rooftop of a drive-in in San Antonio. There was Sahm and Meyers's Sir Douglas Quintet. And they've collaborated on each other's projects from time to time.

Last December, they got together and played a night of Tex Mex tunes at Boz Scaggs's club, Slim's, in San Francisco. And, says Sahm, "it seemed to happen." They recorded "Texas Tornados" (Reprise) in March, filmed a video in April and hit the road in June.

"You know, it's really unbelievable what's happening, man," boasts Sahm. "People are singing Spanish and they don't know what it means. People are waiting outside when our bus arrives, cheering. And we don't even have a hit single!"

The Texas Tornados are performing at the Birchmere tonight at 8:30. Tickets are $17.50 and available at TicketCenter. For information, call (703) 549-5919.