Charles Mingus is an extremist. He doesn't bear with noisy, drunken customers - if they push him to the limit, he punches them out.

But Mingus has never hesitated to push his instrument, the bass, to its outer limits, and to turn it in the '50s and '60s into a frontline instrument when most of his contemporaries were still laying down background rhythms.

It's been more than 20 years since Mingus abandoned the 32-bar popular music form that most jazzmen used then, in favor of an extended form approach, in such pieces as "Pithecanthropus Erectus," that allowed a soloist to improvise as long as he wished. He also helped introduce programmatic sounds - as in the fog horns and whistles of "A Foggy Day," which evoked the soup of London, even though he hadn't even visited the city at the time.

Now, Mingus has the status of a jazz giant - he's worked with Kid Ory, Art Tatum, Red Norvo, Lionel Hampton, Charlie Parker, Dizzy Gillespie, Miles Davis, Milt Jackson - and he's held out against the temptation to dilute his music with rock and electronic influences.

At 262 pounds, Mingus is as imposing as his music. Seated, he sometimes looks like a coiled Buddha about to leap into action.

He's overweight and suffering from a slipped disc. His walk, aided by a cane, is a lumbering, weary gait. Down from 312 pounds, he hopes to reach 187 on his 5 feet 9 3/4 frame.

A master of the put on, Mingus has lampooned former Arkansas Gov. Orval Faubus in a piece called "Fables of Faubus." Many who have followed him closely, however, say his frequently outlandish statements are probably defensive measures.

"The Watts riot was a fake," he says with finality. "I know everybody drove up with some strangers and they did the burning."

In the last decade, this highly complex man, who has been called the Segovia of his instrument, has been unusually quiet, verbally and musically. It was assumed that Mingus was mellowing.

But the 55-year-old Mingus insits that he isn't. And he may have set out to prove himself by threatening to walk out before his Jazz Workshop group took the bandstand at Wednesday's opening night performance at the Cellar Door.

The well-known Mingus temper - the one that has caused him to lecture noisy audiences on etiquette and big social issues - almost exploded. His musicians were late and someone had forgotten to bring Mingus's music from New York.

Muttering "Cancel out," as he trudged out of the club, Mingus asked for Sue Graham, his manager and wife. A few minutes later Mingus returned, calmer but still without his bass music.

He used pianist Bob Nelcom's score, spreading it out over four music stands. "I don't remember the things I write," he mumbled to the audience, "because if I did I wouldn't be able to write anything else."

Despite the delay, the music went on and Mingus had no problem in playing ensemble or solo parts. The music he had composed swirled about the crowded room in different shades and tones, but all one color - blue.

He is a master at making variations on the blues, and his men successfully took up the challenge on pieces like "Noddin' Ya Head Blues," inspired by railroad bums and hustlers, and two gospel-oriented pieces from the '50s, "Better Git in Your Soul" and "Wednesday Night Prayer Meeting."

Except for Danny Richmond, Mingus' percussionist for 20 years, the current edition of the Jazz Workshop is not as high in quality as some of the earlier models.

Trumpeter Jack Walrath is a competent ensemble player but an unimaginative improviser, and Neloma bangs the piano more than he plays it. Tenor saxophonist Ricky Ford, 23, showe flashes of brilliance, but he's still learning.

After several quiet years in the '70s, Mingus says he is perfoming with renewed creative energy.

"I must be getting my energy back," he said shortly before his group took the bandstand. "I'm writing more now - doing some things that Bird (alto saxophonist Charlie Parker, a founder of modern jazz) might have been doing if he'd lived."

Mingus says he's just been through his most trying decade. In 1966 he was evicted from his Lower Manhattan loft for nonpayment of rent. Five years later, 60-minute documentary was shown on televison of that grim November night.

In the documentary he's shown wandering through the disarray of his possesions. The memory of that experience is still harsh, and his tone becomes bitter when he talks about it.

"The city marshals said they had orders to destroy my things, and that's what they tried to do," he said softly, "my coin collection was taken - and I had a coin going back to 1470. My pipe collection. My recording equipment, which was professional, was damaged. My music scores were thrown out on the street. They pushed my grand piano down the stairs.

Several years later, Mingus recalls, he was rebuffed in his attempt to start a music school where children could study jazz. He said Buddy Collette had promised to come East from California, leaving a busy - and lucrative - round of studio work in Hollywood. Sonny Rollins and Britt Woodman were also scheduled to teach.

"I had the place at Third Avenue and 14th Street," he recalled. "It was a block long and half a block wide. Then I started having problems with the urban renewal people. Somebody had read my book (the autobiographical "Beneath the Underdog") and thought I was going to start a whore house. They read about prostitutes and pimps in my book and thought I was going to pull a gangster act on their kids."

Mingus continued: "For five years I didn't want to think about music. I played the piano a little. I didn't touch the bass. Just this year I'm getting my energy to start writing again. You asked me how I started writing again. It's a long story."

Mingus is dieting, and he's stopped eating meat and drinking liquor.

But finding young performers who can play his music is a problem he continues to face. "A lot of young guys can play fast," he noted, "but they don't understand that a jazz solo is supposed to be a composition.They don't know how to develop a piece in a musical sense."

Mingus also complains that blacks don't follow jazz anymore. "They've been brainwashed," he said. "The music didn't change. The people did. Most jazz fans today are Europeans and Japanese."