Benny Goodman's spacious penthouse apartment, looking out over Third Avenue, is cluttered -- but not with the ephemeras of a glorious past, which is what one might expect of a man whose coronation as the King of Swing took place more than 50 years ago and whose reign has not yet ended for countless fans.

To those fans, Goodman remains the Pied Piper of swing, a vivid symbol of joyful, exuberant rhythms and better times than these. What fills this room, though, is an anticipation of present and future challenges.

Goodman's time- and travel-battered instrument case lies open on a couch, the famous clarinet at this moment disassembled and curiously helpless. The score to a Brahms sonata lies open on a coffee table, testimony to an hour and a half of morning practice in anticipation of a classical concert in a few weeks' time.

On the stereo system, now silent, there's a jumble of cassettes, including two recent Goodman projects -- one classical, with the Berkshire String Quartet (private '60s recordings just now being made available); the other a soon-to-be-released recording with the big band that he will bring into the Kennedy Center tomorrow.

On top of the piano that dominates the living room sits the score for "Benny's Gig," a piece for clarinet, bass and violin written by the respected composer Morton Gould. "It's not really new, but I just never got around to it," Goodman says. The Swing King is also a prince among modern classicists, not just for his superb playing but for the works he has commissioned from such composers as Aaron Copland, Be'la Barto'k and Paul Hindemith.

Sitting back now in a chair, the owlish Goodman looks less jazz royalty than feisty patriarch. The rimless spectacles were long ago replaced by horn-rimmed glasses. His eyebrows seem perpetually raised, giving him a faintly quizzical look. At 76, he's just this side of taciturn, secure in his own place in the history of American music, grumpily opinionated about the current state of that music.

As the first musician to successfully bridge the jazz/classical dichotomy (he recorded the Mozart Clarinet Concerto with the Budapest String Quartet in 1937; it's just been reissued), Goodman has few kind words for the latest Wunderkind of two worlds, Wynton Marsalis.

"That's a joke, really," he says, his voice hoarse, his manner detached. "He's so undernourished, really, as a trumpet player. I don't think he's either a classical trumpet player or a jazz trumpet player. He does them quite badly, both of them, and gets along very well."

Goodman, whose own playing has always been defined by dexterity, discipline and imagination, has no qualms about sharing his opinions. "At my age," he says jovially, smile permanently skewed from the positioning of the clarinet, "why the hell not? I'm the first one to acknowledge talent, and I have all over the place. But I'm not going to be psyched into all that hype crap."

For half a century now, of course, Benny Goodman himself has been comfortably settled into the limbo between hype and acclaim. After all, when he ushered in the swing era with his big-band appearances on NBC radio's "Let's Dance" in 1934 and a cross-country tour in 1935, he also became one of American popular music's first media stars. Benny Goodman and his fascinating rhythms were inspiring riots at the Paramount more than a decade before Frank Sinatra. Goodman's career, one of the longest in terms of activity, is also one of the fullest, from his work as a sideman and soloist in the '20s to his tenure as the world's most popular band leader in the '30s. The list of those with whom he has played is a virtual Who's Who of Jazz. He also became the first major artist to break the color line separating black and white musicians when he hired Teddy Wilson and Lionel Hampton in the mid-'30s.

Because he's survived and thrived as long as he has, of course, Goodman has had to endure the most stringent of comparisons: to himself. There have been times when he's been disenchanted with his own performance, times when his inspiration seemed to wane and his invention become stale, even as his formidable talent persisted. He knows he won't play any particular tomorrow the way he did all those yesterdays.

"I can't," Goodman says in a genial growl. The stamina is not there, he concedes, "considering what we used to do at the Paramount . . . seven shows a day, seven days a week!"

Still, he adds, "what you lose in physical -- I mean, just standing up with a goddam clarinet at my age! -- you gain in some other way, I think. In a sense it's easier for me to put a band together now, providing I have the right material. On the other hand, my ass hurts harder when I try to stand up for two hours.

"But you manage that, you know."

He pauses a moment, considers.

"I just don't think I ever lost my enthusiasm for music."

Or his enthusiasm for living in the present tense. "Occasionally I listen to the old recordings, particularly when I got this band together, to compare a little bit, see what the hell I'm trying to do. I don't miss anything . . . Listen, you've got to change in 50 years. That's one quarter of the life of this country. That's a hell of a long time . . .

"I like what I hear," he adds, "but I couldn't do it, it'd be silly. I never knew one solo from another, anyways. I don't mind what I'm doing now. I have my own criteria.

"I tell you one thing . . . I wouldn't be out there if I couldn't play."

Just a few years ago, many of Goodman's fans and friends assumed he had made a quiet retirement. It wouldn't have been that much of a shock. He was already in his midseventies and had had a series of operations, one for a back problem that had plagued him for decades, the other for a potentially fatal aneurism. ("They're no fun.") Goodman's problems forced him to abandon the concert stage for more than two years, and there were reports that he had stopped practicing (though there were private jam sessions at his apartment).

"But then I said, well, if I'm going to go, I'm going to go playing."

Starting last February, he began making a number of unannounced appearances, including one at the Kool Jazz Festival tribute to his brother-in-law, producer John Hammond. Everyone was surprised, Goodman says, "including me." In October, he taped a special for PBS called "Let's Dance: A Television Salute to Benny Goodman" (it will spearhead PBS' annual fund-raising drive in March).

Those recent performances were notable, if only because, as Goodman puts it, "I don't like festivals and I never really wanted to go on television because that's not really the greatest place for a band either . . . the lights are so hot . . . the sound is god-awful."

As Goodman struggled to return to form, and struggled against the wear of time, weren't there moments when he was discouraged? "It's always discouraging when you're trying to play good music, it's a life of discouragement," he says. "But that's the way it goes. In the first place, you've got to meet that instrument every day in practice if you're serious about it . . . "

But now, he says, getting ready for his daily swim at a nearby pool, "I feel pretty good."

There are a few concerts in the works, both big-band and classical, mostly fundraisers. He wants to finally record the two Brahms sonatas. "I've got my work cut out for me."

Benny Goodman has never been one to speak kindly of latter-day pop styles, though an argument can be made that his brand of swing was every bit as much a protest (against the "sweet music" of the '30s) as rock 'n' roll was in the '50s (against bland pop).

"I didn't like it," Goodman says, pointing out that he once led a band for crooner Russ Colombo ("people forget that"). "How do you get to play good music? If you can't find a good [style], get your own."

His transformation from a precocious virtuoso in knee pants (Goodman made his professional debut at 12, joined the musicians union at 14 and dropped out of high school at 16 for the jazz life) to a big-band leader whose music swung the nation for a decade was chronicled badly in Steve Allen's 1955 bio film, better in Goodman's autobiography, "The Kingdom of Swing." Of course, that was published 47 years ago. "It is rather ancient," Goodman chortles, adding that he has no great desire to update it. "Not that I don't think certain things are nostalgic and wonderful."

Since dispersing his big band in 1944 (there have been short-term variations and revivals ever since, mostly smaller ensembles), Goodman has worked pretty much as he saw fit, moving comfortably between jazz and classical music, collecting dozens of degrees and honors (including a Kennedy Center Honor in 1982). Later this month, the Grammys will bestow a lifetime achievement award on Benny Goodman.

Both the PBS television show and tomorrow night's concert will focus on the composing and arranging of Fletcher Henderson, the overlooked black composer and arranger who was one of the great pioneers of big-band jazz. "There's nobody better, is there?" Goodman asks.

Henderson's own big bands in the mid-'20s and early '30s inspired Goodman, and in 1934, he hired Henderson as his principal arranger, a relationship that would continue off and on through 1947. Henderson, whose style was a brilliant meld of improvisation and arrangement, died following a heart attack in 1952 and his reputation has eroded steadily since then.

Yet it was Henderson's brilliant, challenging charts that helped establish the Goodman band (many of the same arrangements had been used previously by Henderson's own band). And when Goodman's first cross-country tour in 1935 seemed destined to become a disastrous washout, it was Henderson's book that came to the rescue late in the opening night at Los Angeles' Palomar -- a date often called the opening night of the swing era.

"He was a great man, one of the key figures in jazz," says Goodman, "and I think his place has been completely forgotten in this whole melee of black composers. He doesn't have any disciples to speak of, whereas there's always a band somewhere playing a tribute to Count Basie or Duke Ellington -- and thank God that somebody is still playing their music.

"It's hard to do a tribute to Fletcher. I hope we've succeeded, I really do. To me, he was the greatest arranger of the whole bunch . . . He had this genius about him, and he was tuneful. When he came in with an arrangement, it was really an occasion. Everybody'd be just knocked out, and then of course, we'd have to learn it."

Goodman rehearsed his new band for eight weeks, which suggests that he's as strict a disciplinarian now as he was half a century ago. "I want a band to start and play together," he notes. "That's not being overstrict." His old bands, he says, "were wonderfully principled and strict themselves. They got to be just as bad as I was. There were quite a few qualities about those men that I find disappearing nowadays."

The problem is not endemic to jazz, he adds, pointing to the recent reissue of his 1937 Mozart concerto with the Budapest String Quartet. "Even they played it quite completely differently than anyone today -- a different tempo, no schmaltz, a straight-ahead kind of performance. I defy you to hear string quartets playing like this now."

There will not be, Goodman insists, a 50th Anniversary Carnegie Hall Concert (there were 30th and 40th anniversary events celebrating the first -- very influential -- jazz concert there in 1938), or any other nostalgic celebration. "No, I've done enough of those. Holy Christ, who needs it?"

Certainly not Benny Goodman.