MR. SATURDAY NIGHT (1992) *** 1/2

Language is constantly inventing or reviving expressions. Two current ones are illustrated by comedian Billy Crystal playing comedian Buddy Young, Jr. and dedicating his life to in-your-face jokes that keep pushing the envelope.

Created by Crystal in 1984 for HBO and repeated on "Saturday Night Live," Buddy now gets full, favorite-comic treatment in Crystal's excellent directorial start. The character is fine honed, assuming you can say this about someone whose humor is not exactly Wildeian or Shavian.

"Mr. Saturday Night" is the biography of now-aged Buddy and his brother Stan, told in alternating flashbacks and flashforwards, with nearly equal time given to the present.

The two Yankelman boys are broad, in-house comics who keep their family in stitches. At their first public appearance on Amateur Nite (sic), Stan, 18, gets cold feet, but remains in the wings, encouraging Abie, 16, who, at the last second, has taken on the name of Buddy Young, Jr.

Nice, quiet, sensitive Stan, stays on with the raucous Buddy as the latter serves his apprenticeship and reaches specialized fame in the Borscht Belt's circuit, culminating at Grossinger's in 1950.

While Buddy convulses his audiences, Stan, in the background, is a perfect definition of "factotum." He is Figaro to Buddy's Count Almaviva, his manager, gofer,soundboard, as well as the butt of his brother's whims and ego. Occasionally too becomes an unwilling, resentful pimp, as when he brings to Buddy an admirer, Elaine (Julie Warner). Stan is attracted to her but it is Buddy who marries the charming young woman.

Buddy rises to becoming an increasingly important Las Vegas performer, though always billed below the headliners. In a clever bit, his appearance on the Ed Sullivan show is a catastrophe, since he follows the Beatles before a frenzied, hysterical audience of youths. Still, he does get TV celebrity as "Mr. Saturday Night," though never attaining superstardom.

Actors never stop acting in real life, but this isn't always evident. Most comics are non-stop performers too, but the nature of their trade is such that their off-stage jokes are always obvious.

Buddy, if not the ultimate, is the archetypical New York Jewish comedian, conceived, written and played with great inside-track knowledge and much affection, colossal warts and all. He is a monomaniacally compulsive jokester 24 hours a day, to the point that only one-liners and gags count for him.

Being so set in his tunnel-vision ways, he becomes self-destructive, flubs his chances, loses sponsors and exploits even those who love him (brother, wife, daughter), through neglect and jokes at their expense. Anything for a laugh, any time.

Buddy's compulsive, incessant joking does not spare events such as his wedding, the birth of his child, his being at his dying mother's side, even her funeral too. Yet on those occasions the film manages sometimes to transcend the tacky and the crude, and can introduce bittersweet moments of true pathos.

The movie is a two-hour homage to generations of ethnic jokemeisters and their shticks. It would take a computer to analyze all the ingredients, the name comics who enter this amalgam. Yet, Crystal's Buddy is both a composite and a comic in his own right.

But he is no human being by common norms. Like many one-track-mind professionals, he is self-centered, has no personal dimensions, or, for that matter, a meaningful private life. In vague terms which place much of the onus on Buddy, we learn that his daughter's life has been a failure.

His wife, the lovely Elaine, was introduced in 1950 as the perfect mate: witty, gutsy, lively with repartee... Later though, when we meet her repeatedly, she has receded into the background. Her personality has disappeared.

Whilst all those around Buddy fade into stooges or supporting characters, the movie makes an exception by sketching with deft irony and much affection Buddy's mother, thus salvaging some family values. Mostly though, it shows with sharp realism the perpetual insecurity of showbiz people, even at the height of their reputation.

Above all, the movie works in, as its second major, as well as most original element, the Buddy-Stan relationship, ambiguous yet clear, built on narcissism and monstrous insensitivity on one side, antagonism, devotion and frustration on the other, and a weird kind of love under the surface.

As Stan, David Paymer quietly steals every scene he appears in. When, "tired of shlepwork," he retires, the film almost acquires a tragic tinge. It is an Osca-caliber performance. Billy Crystal's supercharged acting is striking too, as a monochord, more obvious tour-de-force.

The excellent playing extends to the supporting actors: young agent Helen Hunt who tries, against the comic's own self-defeating nature, to give the aged Buddy a second chance; Jerry Orbach as her boss ; or Ron Silver as a big-time film director who used to idolize Buddy.

The gallery of characters is also reinforced by the precise physical casting of two youngsters as the teen-age brothers, and by the make-up of Stan as an old man. Parchment-faced Buddy however, in spite of the much-advertised, lengthy cosmetic sessions, made me uncomfortable. It felt as though the eyes were peering from behind a plastic mask

The story's structure tends to be a bit systematically repetitious. It hammers its points, especially the swinging pendulum between rapport and alienation in the two brothers. In the last act you sense that the writers are desperately seeking a wrap-up. And since movies cannot let go of the odd notion that performers, whether young or old, deserve more pathos and sympathy than anyone else, "Mr. Saturday Night" too oversentimentalizes the actors and the showbiz profession.

As they should, the jokes run realistically from crude to indifferent, with occasional fresh gems. Equally true-to-life is Buddy's repertory, strong on insults but cautious on political issues.

A hilarious, lightning-fast scene with bread rolls would have made Charlie Chaplin proud of Crystal. But there is much more than rib-tickling to this suprisingly complex and ultimately affecting view of a lifetime in schlock.