Nearly three months after a title defense in which Korean challenger Duk Koo Kim was injured fatally, Ray (Boom Boom) Mancini, World Boxing Association lightweight champion, will fight a 10-round nontitle bout against George Feeney of Britain in San Vincenzo, Italy, today.

Kim suffered severe brain damage when he was knocked out in the 14th round of the championship bout against Mancini in Las Vegas Nov. 13 and never regained consciousness. More recently, Kim's mother committed suicide.

The 21-year-old champion from Youngstown, Ohio, who is an aggressive fighter, has said he feels ready to fight and doesn't think his style will be affected.

"Boxing is sometimes pitiless," said Mancini. "You must hit your opponent and possibly knock him out to avoid being hit. It's a problem of survival. I decided to continue boxing, which is the job I chose, and once in the ring I will punch as hard as usual."

The bout against the 25-year-old British lightweight champion in an indoor arena will be televised live on NBC's "Sportsworld" (WRC-TV-4 at 3 p.m.) . . .

Arthur Boynton, the 61-year-old would-be pugilist, decided against fighting a man 40 years his junior in a Golden Gloves bout because a doctor determined the "golden-ager" could be hurt.

Vermont Boxing Commission Chairman Bernard Cummings said the commission advised Boynton to call off the fight after reviewing the results of medical tests. Boynton agreed.

Boynton, of Orford, N.H., was judged to be an amazingly fit "golden-ager" but not suitable for the highly competitive world of the Golden Gloves. Boxing Commission physician Henry Schmidek, who analyzed medical tests given Boynton Friday, said Boynton was in good condition for a man his age and could safely compete in almost any other sport--but "he might not be in shape for a contact sport."

Schmidek said the commission and the 6-foot-3, 214-pound Boynton agreed the threat of serious injury from a head blow was too great.