"What difference does it make?" asks "Blue" Lou Morini. "If someone has a natural gift and gets up there and does it, what does it matter whether he studied for 20 years?"

Morini has studied for 20 years. He is one of America's leading saxophone players, able to write his own ticket (in six figures annually) when it comes to accepting musical assignments.

But the "naturally gifted" pair he is talking about are John Belushi and Dan Aykroyd, who just get up there and do it as The Blues Brothers, with Morini as a member of the nine-man band.

"They treat the band like we're the stars," says Donald "Duck" Dunn, who has been playing bass with the stars since the heyday of Elvis Presley. There is a trace of something like hero-worship in his soft, southern voice -- or maybe something like an admiration that he knows is mutual.

All the members of the remarkable band who have gathered around Belushi and Aykroyd -- for the 1979 album, "Briefcase Full of Blues," for the movie "The Blues Brothers" and now for a month-long national tour including last night's concert at Merriweather Post Pavilion -- take The Blues Brothers seriously as musicians. Otherwise, they say, they'd be back in Los Angeles or New York or Memphis making money -- not in Columbia, Md., wondering whether rain would dampen the crowd.

"You have to take them seriously," says Dunn, "because they're serious about it. Just look at Belushi -- he's as serious as cancer."

Horn player Tom Scott -- who records for CBS, is currently producing an album for Chevy Chase, and composes for TV in his spare time -- thinks they were serious "right from the beginning." Belushi and Aykroyd "were both closet musicians," he says. "John played drums in 'Lemmings' [the National Lampoon's stage-show parody of Woodstock]. They played at the Mudd Club before bringing it on television."

Morini regrets that the Blues Brothers phenomenon was not more carefully planned: "It just happened," he says of the act that started on "Saturday Night Live" as a comedy bit. "And now they're locked into this caricature." n

The caricature is both musical and personal, Morini believes, and others in the Blues Brothers' 44-person traveling entourage make a special point of assuring anyone who will listen that Belushi is not really "like that" off-stage. The description of Belushi and Aykroyd putting on the roles of Jake and Elwood Blues sounds like a runaway case of "method" acting. "When they put on those suits," says Dunn, "they are Jake and Elwood. That's what they call one another -- even backstage."

Morini has worked out a theory of Belushi's psychology. "John has a great moral sense," he says."He's very sensitive to people and just can't do the superficial, social, mannered kind of relating with a wide variety of people that is inevitable in his position.

"I can play this kind of game, but my wife can't and neither can John. So he has set up this stereotype and he withdraws behind it when he can't handle a social situation. He has a real problem, now: He can't walk down the street in New York without people recognizing him and latching on to him. And it doesn't help him to put on shades, either."

The band comes together from many directions, musically and geographically: New York, Los Angeles and Memphis are their main home towns, and their musical dialects range from country to jazz, with plenty of mainstreat in between. The group that made the first Blues Brothers album, "Briefcase Full of Blues" (which hit No. 1 on the charts in the spring of 1979) was hand-picked by Belushi and Aykroyd. "Duck" Dunn and guitarist Steve Cropper, for example, were chosen because Belushi and Aykroyd had admired their work with Booker T. and the MGs, Otis Redding's backup group.

As individuals, the members of the group can be heard on many albums (Morini, whose main interest is jazz, has just finished working on "Hello Dolly," with mixed feelings) and on soundtracks -- including the album from "The Blues Brothers" movie, and a third LP to be made live at the Aug. 2 Los Angeles concert. The horn section, piano and drums are all veterans of the "Saturday Night Live" band.

There is a kind of disarming spontaneity in the band members' mutual admiration; some of them have played together before the Blues Brothers came along, but on the whole they tended to operate in separate, watertight compartments and they are still a little surprised at how well they sound together.

"It's amazing that it works at all," says Morini. "These cats are coming from so many different places, and each of us really believes in what he is doing. Then there are Johnny and Dan, coming from still another place.

"Actually, we had worked together very little before doing the movie. We had a week of rehearsal before the first album, then nine days of concerts, ending up in Carnegie Hall. But that doesn't matter when you're up there on the stage, knowing that your're standing among so many great players. You're proud to be a part of it, and you give it your best."

There were a few appearances between the album and the movie, but the film and the current tour, which will end on Aug. 2, were the first long stretches of working together. Morini doesn't like living in hotels and traveling overnight from Columbia to Saratoga Springs, N.Y., where they will be this evening, but he says "The gigs are really the saving grace."

Besides the money, which is good and the Belushi-Aykroyd fan club which supplies mass audiences, what brings this diverse group of musicians together is the blues, a root language common to country music and jazz which is the basic American musical idiom and a vocabulary in which the diverse musicians can talk to one another. It is happening behind Belushi and Aykroyd because the sessions on "Saturday Night Live" have imprinted the name and the sound of the blues on the consciousness of millions of Americans.

"As good as these musicians are," says Scott, "we could not have just gotten together without John and Dan, given ourselves a name and gathered audiences like these.

"Of course, with all due respect to John and Dan, we do give them credibility."

Momentarily. It is all momentary, and in another month the Blues Brothers' band will be dissolved into its disparate ingredients, flying back to New York and Memphis or settling down again in Los Angeles. "By that time," muses Dunn, "this band will really be somthing. Right now, it's a baaad band."

Will they get together again? They think so, hope so. But that depends on the inscrutable forces of the music market. Meanwhile, even Dunn (who enjoys touring because "it breaks the studio routine") is not eager to extend the tour beyond its natural conclusion. "If we did it day after day for years," he says, "it would go stale."