People wince when they see Greg Sanders launch his off-balance, southpaw jump shot - the one that makes his nervous St. Bonaventure coach yell, "Oh, no, Greg. Please, no . . ."

But that is exactly what people have been saying to Sanders all his life. He stopped listening to "No, Greg," when he was 12.

Today, Sanders is a graceful, stylish, 6-foot-6, nationally known basketball star. Preseason All-America lists say: Sanders, forward. Sports Illustrated ran two color photos of him last week as one of the nation's five most dangerous college shooters.

Last week, Sanders rolled back to his old haunts around 58th and Eastern Avenues in Fairmont Heights, just across the District line.

The 21-year-old senior's spanking white customized van - with everything from CB to TV inside and "Mr. G" in silver on the outside doors - looked out of place in the parking lot of Melvin's Crabhouse.

But Sanders knew this was the right place to say, "Thank you," on Thanks-giving. It was Melvin - Melvin Roberts, that is - who took Sanders under his guardianship 10 years ago and told him, "Yes, Greg. You're a little go-getter, I can see it. You always answer the bell. A worker like you can do anything in life."

From the time he was in the sixth grade, Sanders worked like a man at the crabhouse, and at other odd jobs.

"The kids around here don't have much," says Roberts. "But Greg always wanted to work to have his own. He'd dig into any job and he'd always ask, 'Mr. Roberts, can I get some extra hours?"

The young Roberts, described by many as a generous "neighborhood father," took a unique interest in Sanders, becoming his guardian and paying his way to private school at St. Anthony's.

"Lord, don't say Greg's family was poor," says Roberts anxiously. "His mother will chew my head off. 'My children always had food on the table and clean clothes on their backs,' she'll say, and she's right."

Certainly, Sanders did grow up in a family of nine in two rooms over a liquor store, but, as Roberts says, "That gives a wrong impression. People hate the word 'poor.' You don't have to be well-to-do to have pride and deserve respect."

Nevertheless, the "No, Greg" refrain seldom ceased during his adolescence. No, Greg, a sixth-grader can't work like a man. No. Greg, you can't cut it in private high school. Why bother driving across town in that old jalopy every day to get tutoring?

Forget about a major college scholarship, Greg. Nobody wants you. You didn't come close to making All-Metropolitan, not even third team. Stop sending those clippings and grades all over the country. You can't talk your way into the big time.

But Sanders did crash St. Bonaventure's rebuilding program: Coach Jim Satalin now calls him, "My easiest recruit. He recruited me."

But once in college, the deprecation, the "No, Gregs," increased. Roberts looks around the walls of his recreation room at the photos of youth teams that Sanders played on. "College beat a lot of 'em," he says. "Greg did everything to get himself ready."

Roberts points soberly at one of Sanders' playground mates in the photo. "He's still on heroin," he says. "And that guy. Yeah, he's the one who drank the quart of antifreeze and killed himself."

"Growing up in Washington, it's hard to find out how good you are," said Sanders. "Super players . . . the town's full of 'em. For long time, they wouldn't even let me on the court."

When college time came, Sanders wanted to leave town. Every other outstanding St. Anthony's player of the early '70s followed coach John Thompson to Georgetown.Sanders, who has proved to be the best of the lot, was the one exception.

It was Washington, not Georgetown, that Sanders avoided. "Your old friends," he says meaningfully," don't always help you."

Sanders heard enough carping from his peers even in New York. "Grey, why are you going to summer school every year? Your grades are good. What do you mean, 'I want to stay ahead of the game?'"

Sanders was not supposed to have a prayer of starting as a Bonnie freshman, but jumping off the bench in the season's first game, he sank 10 of 13 shots and won a job.

His two dominant traits as a player were evident immediately. He played best against the toughest opponents, and he worked fanatically to improve each year. His scoring average (17.5, 18.8, 21.2) and shooting percentage (.518, .559, .584) rose each season.

"I have common sense and I know my weaknesses," said Sanders. "I improve. That's what I'm proudest of. Some players never stop making the same old dumb mistakes. Every part of my game can become better than it is. I hope I'm not at my peak."

Sanders' limitless ambitions, his quick smile and his complete confidence keep taking him to new "No, Greg" peaks.

"It's important to be independent," said Sanders, and he means financially independent.

While taking summer-school classes to get next year's grades ahead of time, Sanders is simultaneously earning money as an elementary school teacher. "Math, social science, everything," he said, and a disc jockey.

The day summer school ends, he is back in Washington at the crabhouse "getting funky and crab-smelling."

"He's a big shot now, but he doesn't have a big head," said Roberts. "He'll still take the dead crabs out of the walk-in box, drive 'em to the dump and then scrub out the truck.

"He loves to work the takeout window because he gets along with everybody. Out of all the fools who might come up to that window, he doesn't get mad at anyone. He just says, 'Thank you.'

"He's like that on the court, too," added Roberts. "They talk that street jive to him and he just smiles and puts up one finger as soon as his shot is gone. That means, 'Count it.'"

In fact, Sanders knows how to talk a little cordial jive of his own. He can't wait to play host to Georgetown next Saturday. His high school coach, Bob Grier, is now a GU assistant.

"I'm going to smile and say, 'Hello, Mr. Grier,' said Sanders mischievously, "then I'll whisper '45 points.' That'll get him thinking."

Sanders' flamboyance on the court, his love of style, is all part of a spontaneous confidence.

When the Bonnies reached the final of the NIT last spring against Houston and its reknowned Otis Birdsong, the crowds at Madison Square Garden were whispering, "No, Greg," once again.

In the biggest game of his life, Sanders had the best game of his life. "I was in another world," he said, squirming in his chair with delight at the memory. "I was going crazy.The spirit moved me, I guess. My mind was going and going, telling me, 'This is the thing you do best in the whole world. Explode!"

In the final seconds, with the Bonnies behind by a point and the game on the line, Sanders exploded one last time, firing and outlandishly awkward-looking jumper from well beyond the circle.

Satalin leapt to his feet, and perhaps for the last time, someone yelled, "No, no, Greg . . . Yes, yes, yes.

Sanders' career-high 40 points (on only 23 shots), plus a game-high 12 rebounds and six assists, gave the Bonnies the championship and Sanders the totally unexpected MVP award.

Before that game, only one NBA type - sharp-eyed Red Auerbach of the Boston Celtics - had contacted Sanders, chatting with him all of one afternoon. In its aftermath, Sanders had six-figure salary offers - relayed to him by intermediaries - from several NBA teams, who said they would draft him if he went hardship.

"I owe too much to St. Bonaventure to quit before my last year," said Sanders. "I'm way ahead in my credits and I will graduate with my class, and not too many athletes pick up tha diploma the same day everybody else does."

Nevertheless, Sanders worries about this senior year. "All eyes are on him," said Roberts. And all defenses will be, too, now that the Bonnies' other 21-point scorer, Essie Hollis, has graduated.

"This is my last year to get it all ready for the pros," said Sanders. "After all these years. I'm this close to making it," he said, not having to add that like every college hotshot he is also just that close to not making it.

"At nights sometimes I'm almost trembling, thinking, 'How will I be in the future?'"

For the present, Sanders is exactly where he has always planned and worked to be.

His clothes are of fashion-model quality - simple in style, dramatic in impact. The other reward Sanders has given himself for all his long hours of shoveling dead crabs, scrubbing floors, emceeing teenage dances, teaching school and spinning records is that brand new customized van that replaced the '66 Buick in the crabhouse parking lot.

Sanders know that some people will look at it and say, "Another college athlete on the take." Others will see the tape deck, the plush red interior, the idirect lighting, the telephone and see another superficial young basketball player fascinated by the Walt Frazier supercool style.

"I try to accept other people as they are," said Sanders. "The affluent and the destitute," he said, pleased with his turn of phrase, "I know 'em both. If people don't take me for what I am, it doesn't bother me. It's one them.

"I know this van . . . you know, the Mr. G on the doors and all that . . . may be too much for some people," he said, a little sheepishly. "But I earned it," he said proudly. "Maybe I even deserve it."

As Melvin Roberts would say, "Yes, Greg."