Cambridge, Mass. — Norma Jackson kept her son, 9, out of school just to meet Sugar Ray Leonard, newly retired welterweight champion, who was spending a day at Harvard. Looking more like an undergrad rather than a retired pugilist, wearing a corduroy suit and sporting diamond studded rings on his fingers, Leonard reported to Harvard bearing good will, autographs, and color photographs.
He relaxed most as he chatted informally with children whose parents, like Norma, brought them to Harvard to meet him. Sugar Ray passed out color photos and signed them for the children, Harvard students, and adults.
The Harvard Foundation - organized because minority students on campus cam- paigned for a means of expressing themselves and gaining appreciation from other elements at the university - invited him to the campus.
Sugar Ray was supposed to talk about interracial and intercultural relations. ''I'm not at Harvard to give speeches,'' he said. ''You students at Harvard don't need my advice to get an education. You are here already.''
So he rapped - about boxing, the ''whipping boy'' of sports; about his family (wife and son, 9, his co-star in Seven-Up commercials); about his future in television and as a personality, and about Harvard and education.
''I see myself as a part of boxing all my life,'' Leonard repeated and repeated. ''Without boxing I would be an unknown. Certainly, I wanted to go to college - but Harvard, this is the cream of the crop. Just appearing here makes me proud.''
Leonard advises all young people, especially minority children, to get an education. ''Yes, boxing is rough, sometimes dangerous, but it helped me. It gives an opportunity to us who can't pass tests to speak at places like Harvard.''
He has quit the ring virtually unmarked physically, a smiling ambassador of good will for a sport that has come under sharp censure due to some unfortunate occurrences in recent bouts, including the death of one fighter. He likes television commentator Howard Cosell as a man who has contributed to boxing, ''but boxing has helped him, too.''
Sugar Ray describes Cosell as a man ''who uses a lots of big words I don't always understand. He and I get along pretty well, but I don't always listen to him.''
The Sugar Man, named Ray Charles Leonard after the singer, became a boxer out of necessity, and he retired because of a promise he made to himself.
After gaining international fame for winning the 1976 Olympic lightweight gold medal and being the rah-rah leader of the United States boxing team, Sugar Ray came home to reality. He was a father, and he had to start thinking about supporting his family.
When he turned pro in 1977, he recalls, he made a promise to quit the ring ''when I received a message.'' He became undisputed 147-pound champion, a multimillionare. The ''message'' came last summer, he says, through an eye injury in a title bout. He announced his retirement last month. Looming ahead was a match with middleweight champion Marvin Hagler for ''fantastic money.''
A fight with Hagler? ''A great battle,'' he said. ''A big purse - but no one more time for me! I want people to remember me as one boxer who quit and never returned to the ring.''
Asked about Harvard, he quipped, ''I'd like to buy it!'' More seriously, he said, ''Hopefully, I'd like to see my son come here.''
What will his son be? A boxer, too?
''I don't know,'' Sugar Ray smiled. ''He has tried boxing, but he didn't like it. Now his love is basketball. But really, little Ray has no choice. He goes to school every day. He has to study and do his homework.''
Leonard calls his son a ''superstar'' for soft drink ads, but reflects, ''His mother and I limit his commercials and public appearances. We want him to have a childhood. I missed those childhood years.''
Speaking of his own future, Sugar Ray said, ''I once planned to study communications in college, but now I am making it with on-the-job training.''
He works as a sports color man for both the CBS network and HBO (Home Box Office) cable television. He says he hopes to expand his career by owning his own TV network and conducting a general talk show.
Sugar Ray does not plan to manage or train fighters. ''I just don't have the patience,'' he said.
Leonard emphasized before each group at Harvard, ''Be the best - whether in athletics, politics, or business. My talent was boxing, and this brought me fame and money, but personally, I cherish love above all.''