By BRIAN FITZMAURICE

Any bar band can pluck some bass and scream, "Yeah, I feel good!"

A performing group that can, on the other hand, convincingly stretch their limits from James Brown and Joe Cocker to Patsy Cline and Glenn Miller is bound to gran -and keep- your attention. Soulful, rockin' R&B band Mary Lou and the Untouchables does it this weekend at the Jetty Tiki bar at Kent Narrows on the Eastern Shore.

Contacted about the 8-piece band, clubs from Ellicott City to Annapolis and Ocean City all talk about the musicianship of the Untouchables and always come back to the charisma of the lead, Mary Lou Magee.

Keyboard player and co-founder of the band, Charlie Hamilton, remembers first seeing Mary Lou (as she is known) sing in Chaos, a Top-40 band. "She would jump on stage and take over. I thought, "Wow, I'd love to build a band around her.'" Tiring of the Top-40 format, Mary Lou was also looking for a change to the more expressive R&B sound she admired in Aretha Franklin, James Brown and Janis Joplin.

Along with fellow Chaos members John Gleim on drums and guitarist Danny Lough, Mary Lou teamed up with keyboardist Charlie Hamilton, and the Untouchables started taking shape. Mary Lou always wanted a "horn band," so the Untouchables were rounded out with Alan Dahlstrom on saxophone, Saul Strieb on trombone and Bobby List on trumpet. Jay Corey now plays on bass. There are no beginners, the band figures -without admitting individual ages- it has 140 years of collective music experience.

The music is built around Mary Lou's versatile voice and engaging stage presence. "We start with a known funky blues song and expand on it with our own arrangements," explained Mr. Hamilton. "We don't do straight covers."

Like an independent-minded quarterback, Mary Lou reads the audience and calls out the songs to the band on stage -there is no predetermined set list. A wide repertoire, therefore, is understood. Depending on how Mary Lou feels out a crowd, Mr. Hamilton explained: "We may go from the R&B of Wilson Pickett to Lynyrd Skynyrd southern rock, all the way to a swinging 'In the Mood,' or a Patsy Cline ballad. With Mary Lou, we can cover them all, yet we're not a 'variety' band. It's all done within our own unique sound."

The band's spontaneity on stage is not lost on the clubs. "One of the reasons we like them so much," said Don Schroeter, of Junction Station Cafe in Catonsville, "is that they play the crowd, not a set play list." Even without a dance floor, continued Mr. Schroeter, "she packs the place, they come in just to listen."

At the Jetty on Kent Narrows, where Mary Lou and the Untouchables play tonight and tomorrow, owner Bobbie Schock sees the band's crowd-pleasing performance as a sign of professionalism: "You can tell. Bands that don't have it together can be playing on a crowded night and you'd barely know they are there. Mary Lou has everyone on their feet all night, glued to her."

"The Jetty is one of our top spots," said Mary Lou. "I guess it;s the scenery by the water, the down-to-earth atmosphere. The people come out to have a good time and treat us well."

This coming week, from June 19-25, Mary Lou and the Untouchables will appea at the Sheraton Inn in Ocean City. Dr. Leonard Burger owns the inn and books the enttertainment himself.

"We are very excited about Mary Lou and the band. They are the only group we have already scheduled into 1996. That says what we think about them."