MJQ Marches to Different Drummer : Jazz: The venerable quartet finds a replacement for the late Connie Kay in its very own extended family.

The Modern Jazz Quartet takes the stage like a string quartet preparing to perform a cycle of Beethoven works. Dressed in dark, conservative suits or tuxedos, the four veteran players approach their instruments--piano, vibes, bass and drums--with the style and decorum, the calm, professional assuredness of classical virtuosi.

The music begins, quietly at first, then urged forward by a subtle, driving swing that is simple, understated and irresistibly rhythmic. But no matter how much the music heats up--and it does--the quartet continues to retain its cool, relaxed demeanor. The magic of the Modern Jazz Quartet is its talent for cranking up the fires of jazz without breaking a sweat.

Forty-three years after the MJQ was formed, it has become the jazz world’s longest-lived, unerring standard of musical excellence. The ensemble performs tonight at the Cerritos Center for the Performing Arts and again on Sunday after at Pepperdine University’s Smothers Theatre in Malibu. The Sunday afternoon performance is an extremely rare (i.e, microphone-free) concert.

And the MJQ still looks like a group of escapees from a classical recital.

Pianist John Lewis, the MJQ’s founder, mentor, spokesman and primary creative force, laughs when the description is mentioned.

“Well, doing it that way seemed like the right thing in the beginning,” he said, voice cracking in his characteristically halting, but very-much-to-the-point, manner. “And it does now, too.”

As it has since shortly after Lewis, vibist Milt Jackson, bassist Percy Heath and drummer Kenny Clarke got together in 1952, initially to make some recordings. Clarke stayed until 1955, when he was replaced by Connie Kay. For the next 39-plus years, the group remained intact, its continuity interrupted briefly in the late ‘70s when Jackson elected to try his hand as a solo act. But neither he nor the other group members have ever produced outside work with the continuity and consistency of their efforts within the MJQ.

In 1992, the MJQ’s activities slowed down when Kay began experiencing cardiac problems. Last December, the group’s seemingly unwavering stability was shaken when Kay died suddenly at the age of 67.

“It was a big blow,” recalled Lewis, 75, himself recovering from recent gall bladder surgery, in a phone conversation from his Manhattan apartment, “when Connie got sick, first of all in 1992, and then passed away last December.”

Kay and Heath, 72, were the most laid-back, self-effacing members of the quartet, devoting their efforts to laying down a smooth rhythmic passageway for the improvisational excursions of Lewis and Jackson, 72.

Kay brought superior skills, a versatile background and an easygoing bearing to an ensemble whose individual interaction was not invariably as steady as its musical blend.

“Connie was very, very subtle in a way that was hard to catch on to,” Lewis explained. “Even for me, sitting in the quartet with him all those years. I often wondered, for example, what he was doing when we were setting up. He took forever to get everything exactly the way he wanted it to be. It took a very long time to begin to appreciate and understand what he was going for.”

Regardless of what Kay may have specifically had in mind, the amalgamation of four disparate individual and musical personalities came together in a way that no one could have predicted. Music came pouring out in a bountiful rush of imaginative creativity: concept albums, Third Stream recordings combining jazz and classical styles, original compositions such as Lewis’ “Django” and Jackson’s “Bags’ Groove,” dozens of performances and recordings with symphony orchestras, soundtracks for Roger Vadim’s “No Sun in Venus” and the Harry Belafonte film “Odds Against Tomorrow,” appearances and recordings with guest artists such as Sonny Rollins, Laurindo Almeida, Jimmy Giuffre, the Swingle Singers and the Manhattan Transfer.

All of it was energized by the group’s inherent ability to swing, its capacity to remain in touch with the essentials of jazz while exploring the outer limits of compositional structure.

Kay’s passing tested other limits as well. Replacing any member of a longstanding jazz ensemble can be difficult. Replacing the drummer in a quartet with a 40-year resume of accomplishments, a quartet with a collective musical method that can best be characterized as intuitive verging on symbiotic, seemed to be an impossible task.

As it turned out, a potential replacement was startlingly close at hand: Heath’s younger, brother, Albert, who is popularly known as Tootie.

“Through some good fortune--heaven or whatever it is--we found somebody who’s wonderful,” Lewis said. “And he fit into the ensemble almost instantly. But, of course, [this kind of playing] is not something that you can find out about from the outside. . . .”

Heath had very little opportunity to find out about it from the inside, either, before having to go out to the trenches. With barely enough time to get the basic repertoire sorted out, he made his debut performance with the quartet in March at a White House dinner honoring King Hassan II of Morocco.

“It was quite an introduction for Tootie,” said Lewis with a chuckle. “And he carried it off very well.

But not without a certain level of stress on the part of the 60-year-old Heath.

“Man, I had so much anxiety about what to do,” he recalled. “Because basically I’m playing the music that Connie played. I practically had to learn how to play all over again, almost, at half volume. And what I’ve had to keep in mind is that I don’t have the liberties that I have in other group situations.

“So I have to be very sensitive and listen, and I think that’s what the MJQ is about--listening to each other. And that’s a lot different from the kind of improvising where you close your eyes and play whatever you feel, whenever you feel it.”

Has Tootie Heath changed the MJQ’s music in any noticeable fashion? Critical reviews of the group’s first extended run earlier this year at New York’s Blue Note club suggested that he has had a positive impact while remaining within the boundaries of the MJQ style. New York Newsday reported that Heath “. . . possesses a formidable array of resources and instincts that easily flow into the ensemble’s bright, polished and subtly complex musical mix. . . . In short, he looked pretty good up there.”

Lewis has a slightly different take on Heath’s participation.

“Something’s going on here that most groups have never experienced,” he said. “Tootie and Percy are two siblings playing together in the same group. And even though they worked together earlier in their own group--the Heath Brothers--I think they may be more satisfied about this experience.

“The other thing is that they are loving siblings--they really love each other and are very understanding of each other. That’s a very important thing, and it’s a quality that comes out in the music.”

But the most telling evaluation of Heath’s successful integration into the MJQ and the significance of the group’s continuing role in jazz was offered by the nation’s No. 1 Jazz Fan at the above noted White House dinner.

“I still consider them,” President Clinton said, “the greatest music group in history--without a saxophone.”

* The Modern Jazz Quartet performs tonight at 8 at Cerritos Center for the Performing Arts, 12700 Center Court Drive, Cerritos , (800) 300-4345 . The group performs Sunday at 3 p.m. at Pepperdine University’s Smothers Theatre, 24255 Pacific Coast Highway, Malibu , (310) 456-4522.