The busboy is spilling the water even as he pours it, staring at this hulk of a man ensconced at the table.

"Ahhhh, excuse me," he finally says in good Brooklynese, "but ah, are you any relation to John Belushi?"

The Hulk feigns a smile, like Bud Abbott reacting to one of Lou Costello's dumb moves.

"No! No relation!" he snaps. "Anyway, he's a lot meaner than me."

"Jeeeeeze, you look just like him, you talk just like him," the busboy says. "I thought for sure youse was related."

"This woman is married to him" The Hulk says, pointing to his dinner companion. "And I'm her husband."

A year ago, hardly anybody would have noticed John Belushi. He was one of a half dozen Not-Ready-For-Prime-Time Players backing up Chevy Chase on Saturday Night Live. Chase was the new Capt. Midnight of Saturday television, and Belushi was the weird guy who played a killer bee, mimicked Joe Cocker, acted out the demented Japanese swordsman (which last season evolved into a skit called "Samurai Night Fever") and introduced America to the cry, "Cheeseburger! Cheeseburger!"

Then last fall, after Chase left the show, Belushi became the new Goonhead of the "Saturday Night" cult (although Belushi himself thinks Chase's departure moved the show from the realm of individual accolades to real team effort). Last month his television persona was inflated monumentally with the release of National Lampoon's "Animal House," a film that's grossed over $1 million a week to become the third most popular movie in the country. It's the story of a wacko fraternity, and Belushi exorcises the churlish, childish demon on every campus by grunting, groaning, Greeking and geeking his way into the American psyche.

There's something innately comic about Belushi, on screen and in person. He's a borderline fatso goofball, the guy in college who begged the devastating one-liner: Walking out of the lecture hall, passing in front of the professor, and the professor says, "I just had a total eclipse of the class."

At 29, you'd call this guy a slob, a pig, a gross-out king - an image he rarely tries to dispel. When a garage keeper recognizes who he is, and promises a space in his already full lot, Belushi comments, "They like to please the sleaze."

But there's a decided lilt to his lumber, a brilliant bit of temperance and sophistication in his 10-ton delivery - reminiscent of Groucho Marx making an insult so extreme that it became outrageously funny, Buster Keaton turning physical awkwardness into ballet, Zero Mostel and Mel Brooks pushing convention to its absurd limit - all with a decidedly contemporary overlay.

In the film, Belushi carves out a virtually silent comedy sequence that may become a classic, walking through a cafeteria line and grabbing enough food to feed a side show. Here in the restaurant, waiting for a table, he characteristically arches his eyebrows while leering at an innocent bowl of mixed nuts. Then - WAP! - he pounces on the bowl with a speed-of-light hand, gobbling the little guys before they know what's grabbed them.

Without missing a beat he's on his feet, straightening his jacket, cocking his mouth into the orange peel-stuffed countenance of Marlon Brando in "The Godfather." This is an Italian restaurant, and Belushi is saying in Brando's raspy tones, "I'll take care of this guy and get the table." He breaks a breadstick in two and wields it like a switchblade.

Then he's mimicking John Travolta, talking slowly, deadpan kid from da Bronx, "Ya know, John, I just tink the parody you did of 'Saturday night fever' on da Saturday Night Show was da best parody of 'Saturday Night Fever' I ever saw." The words tumble out, each one dropping like a cinder block.

Belushi has a way of instantly assuming any ethnic role, physically and vocally. He seems like a natural method actor, much in the manner of Brando, his great hero. He curls his mouth down and declares. "I coulda been somebody. I coulda been a contender." He's talking about the Russian Turkish bath house he goes to, and his head starts dancing like a bounding gypsy. "You go to the schvitch," he says. "A schvitch is vere you schveat." First Date

Maybe it's the natural instinct of an immigrant's son, this crazy desire to devour every ounce of The Land of Opportunity and then spew it out subjectively. Belushi's father left Albania for Chicago when he was 16, and ultimately opened several restaurants. Belushi's wife, Judith Jacklin - they met in high school at a Little League baseball game - recalls their first dinner date.

"He said we were going out to dinner, and we drove from one side of Chicago to the other to one of his father's restaurants, where he worked as a busboy. I never saw so much food."

"Why are we ethnics always attracted to WASP girls who don't eat?" Belushi asks, wolfing down pasta. "Her parents loved me. I ate everything on my plate. I think it was one pork chop."

In high school in Wheaton, Ill. (where Bob Woodward was one of his schoolmates) Belushi was more serious about sports than studying. He started listening to Bob Newhart comedy records and got interested in acting.

"Newhart had great timing," he says. "He didn't scream or yell, and he didn't make cheap ethnic jokes." (Belushi is guarded about his ethnic background, typically avoiding a question by turning it into a joke: "Most people think I'm Italian," he says. "There are 20 million Italians in this country, so why alienate them?")

After a brief visit at the University of Michigan, Belushi jumped into summer stock acting.

"I did the usual stuff," he says. "Maxwell Anderson, Arthur Miller's 'The Crucible,' but I got kind of bored with it." He moved on to Chicago's Second City, an improvisatory theater company that also served as the training ground for Saturday Night's Gilda Radner, Bill Murray and Dan Aykroyd.

"I worked on this sololiquy from Richard III," Belushi says. "It's a standard thing for actors to do, but I mixed it up with a whole bunch of other soliloquies." He starts intoning an indistinguishable burble of dignified, British-sounding nonsense. "See, it's real impressive." When his name and antics were mentioned to the producers of "Lemmings," a National Lampoon-spawned play, Belushi got a call from New York in 1973.

"I did the soliloquy for them," he says, "And my Joe Cocker imitation, that I had been doing in Chicago." He got the part, went on to direct a traveling Lampoon stage show, recorded several Lampoon records, worked on a Lampoon weekly radio program and eventually was recruited for the "Saturday Night Live" show, along with several other Lampoon alumni. Thoughtful Mind

"I hired him," says producer Lorne Michaels, "because he walked into my office and started to abuse me. He said, "I can't stand television,' and that was just the kind of abuse I wanted to hear."

"I wasn't very nice to him," Belushi says shyly. He's sitting next to Michaels in Elaine's. There's a real sense of repentence in his voice. Although he comes on like a jet-powered lawn vacuum, there's a thoughtful mind at work behind The Hulk. Over dinner he proffers some political concepts, explaining why he backed the Senate campaign of Bill Bradley. "He did us a favor being on the show. So I did him a favor. But most of all, be listens. I told him I wasn't really sure about nuclear energy. I said, 'I'm not convinced we should level the Rockies for oil shale rather than build reactors."

It's a side of Belushi his public rarely sees. "That's kind of my private life," he says, something he hates to talk about, something he guards by throwing out public images of himself as a demented misfit.

At Al & Ann's Luncheonette in his Greenwich Village neighborhood, the counterman shoots him a stare. Belushi responds by screaming "cheeseburger," and then rolls his tongue out like the depraved Bluto he plays in "Animal House." The guy asks him to autograph his check, and Belushi says dryly, "I've been coming in here for years, and it's only now you notice me." People Forget

"There's a big difference between television and movies," he says. "When you're on television, people who notice you will just walk up to you like you're a real person and tell you they thought something you did was awful. But when you're a movie star, they think you're something special. It's like you're in your own world and they're peering in. People forget stuff. We went to get gas the other day, and the guy was staring into the car while he cleaned the windshield, and then he left the Squeegee on the roof. We found it up there when we got home.

"I don't know what I want. I want to keep with the television show, I want to do movies. I want my band (The Blues Brothers: Belushi, Aykroyd and several serious blues musicians who debut on Sept. 9 in Los Angeles, where they will record a live album). I guess I want everything. The trouble with Hollywood is they're all so caught up with themselves. I told them out there that I want to do a Blues Brothers movie. Elwood and Jake. I said it would be a road film, like Hope and Crosby.And they say, 'What will the relationship be between the two guys? And for these Hollywood guys, it has to be real dumb. So you say, 'Elwood is really smart, but he thinks he's stupid, and Jake, Jake is really stupid, but he kinda acts smart; and Elwood decides to follow jake . . .' And these guys say, "Oh, 'that's it." That's how you have to relate to these guys."

Belusi leaves the luncheonette and walks home, an expansive, ornately decorated place he's just bought.

"Welcome to Graceland," he says, and then immediately screams out "Sonny," introducing one of his assistants as Sonny West, Elvis' former bodyguard. Belushi proceeds to play some rehearsal tapes of The Blues Brothers, and starts going through the mail.

"Rick Hutchinson," he says. "God damn, I went to high school with him. Look at this." He holds up a poster of an evil looking fellow who needs a shave. "People send me pictures of people they think I look like." He's reading aloud from reviews of the film, shaking his head in disbelief at the superlatives being tacked on his performance.

You know, I never went to a fraternity party," he says. "It was different back then. All we cared about was rock 'n' roll and staying out of the Army. I was No. 59 in the lottery! A wreck when I went in for my physical, and they told me I had high blood pressure. I was less fanatic than some of my friends. I used to run away from the cops at demonstrations." Last Chance

Belushi decends to the lower floor of his home, past a table that's graced with an old etiquette book.He reemerges with a genuine Bedouin veil a friend has brought him from Damascus. "Doesn't this look like the PLO," he says, wrapping it around his head and adding sunglasses. "You like this?" he asks his cat Samantha. "I got her on my birthday three years ago [Belushi will be 30 on Jan. 24], when I didn't even have $100 in the bank. And now [he shakes his upraised hands to the heavens] Graceland. See what can happen at "America?"

He's going through the papers again - veil off - and notices an ad for on upcoming Grateful Dead concert. "Last chance to be a hippy," he quips, "Take acid and go to a 12-hour concert," then a pause. "You know, you get to be a celebrity and it really changes things. You just have to sit there and go hmm-hmm-hmm. [He looks around as if there are people watching him.] I went to see the Stones here and I'm sitting right next to Paul McCartney. You can't exactly get up and scream 'LIES' [the title of a Stones' song]."

After dinner, outside the restaurant, Belushi starts running down the street like a tackle on the rampage, trying to hail a Checker cab. He misses, and four teen-age girls come up and say, "oh, we loved your movie," and Belushi retorts with a classic line from the film: "Toga," a metaphorical cry of defiance. "Ya wanna go see the film?" he asks them. "It's at the Murray Hill."

Into a cab. Belushi gets in front with the cabbie, and after a few minutes says to him, "CB, huh?"

"Yeah. "I listen to the people drivin' around."

"You got a handle?"

"Yeah, the Bionic Man."

"Mine's the Blacktop Vampire," Belushi says - and he's got his hands cupped over his mouth, racing along with hundred-mile-an-hour CB jargon, interspersed with sound effects of static and interference: "Breaker, breaker - squelch - you got the Blacktop Vampire eastbound - how's it look over your tail - squawk - come on back Vampire - We're looking for that ring of fire - quack - got two bears here in a paper sack. . ."

The cabbie is laughing so hard that he's swerving back and forth on 2nd Avenue. When he gets to where Belushi is going, everybody piles out.

One of Belushi's friends is paying the fare, and the cabbie leans out the window.

"That guy's the funniest person I've ever seen," he says. "He ought to be in show business."