Sylvester Stallone is planning a film on the life of Ray (Boom Boom) Mancini. Because the movies are capable of historical and psychic revision, the script will make little or no mention of Duk Koo Kim, the South Korean boxer who died three days after fighting Mancini last Nov. 13 in Las Vegas.

"We think an 'up' kind of story has more appeal," said one of Mancini's lawyers, Regina Andrielo. The story to which she refers has its antecedents in a sentimental fistic filmography that includes "The Harder They Fall," "Someone Up There Likes Me," and the sport's "Divina Commedia," the "Rocky" trilogy.

This is the story of how a sturdy lightweight named Lenny Mancini ended a promising professional boxing career after being wounded in World War II and quietly earned his living for 30 years in Youngstown, Ohio, as a trucker for the General Fireproofing Co. (Local 1617, AFL-CIO). It is the story of how his son Ray fulfilled his father's dream, winning the WBA lightweight title from Art Frias last year at age 21. Mancini may even play himself in the movie if his schedule allows.

Mancini will defend his title here Thursday night against Orlando Romero, a wiry left-hander from Peru who seems to have impressed only the promoters and the most cautious handlers. The likely scenario is that Mancini will come out full throttle against Romero and wear him down by the middle rounds. (The tape of the fight will be televised Saturday at 4 p.m. by WDVM-TV-9.)

Mancini's camp insists that the "whole Kim thing" became a matter of the past when the young, almost elfin, fighter held long talks with his priest, Timothy O'Neill, and decided to return to the ring. Mancini's handlers are eager to further the career of potentially one of the game's most attractive commodities, although certainly Kim's death and the grief that followed cannot be forgotten by anyone, especially Mancini.

Mancini will earn $600,000 for the Romero fight; future bouts against well-known fighters such as Hector (Macho) Camacho, Howard Davis, Aaron Pryor and Bobby Chacon will be far more lucrative. Already, Mancini has signed a contract with the William Morris Agency. A Chicago toy factory is marketing "Boom Boom" boxing toys--tiny gloves and bop bags.

"I guess (the Kim fight) affected him financially," Andrielo said. "At first it affected his market ability outside the ring. Some endorsement possibilitites stalled because people wondered how Ray's name would affect their product.

"But he certainly became a houseold name for whatever reason. He won a lot of support. People were glad to see someone so young handle something that tragic with so much grace and dignity."

Indeed, Mancini is a likeable, modest man in a world not usually known for those qualities. He looks you in the eye and tells you his cornball story, how he went into boxing, heart, body and mind, to take the title his father never had the chance to win.

Mancini has fought once since the Kim fight, winning a 10-round decision in a nontitle bout seven months ago over George Feeney. Mancini and his handlers worried about whether the Kim tragedy would become a liability in future fights, but he proved able to concentrate and fight with nearly all of his accustomed fire.

"He wasn't as devastating as he is usually," said manager Dave Wolf, "but in the 10th round he had Feeney in trouble and he really went after it. That was the whole thing for us. We wanted to reacclimate him to the ring. The Kim fight is so far behind us. It isn't even something we think about."

As wizened old trainer Murphy Griffith padded his fighter's hands in preparation for a last prefight workout at a Times Square gym, Mancini said thoughts of Kim do not and cannot haunt him any longer.

"Getting in with Feeney, it was like my other fights, no problems," he said, lowering his eyes. Griffith smeared Mancini's face slick with vaseline and the fighter fell silent.

Understandably, Mancini has had enough of talking about the Kim tragedy and its aftermath. Cooperative and poised as he is, Mancini is not about to unleash a primal scream in public. He cannot afford hesitation or doubt. Against Romero he might survive, but against Pryor, Camacho or Chacon doubt could be fatal--metaphorically and, as only Mancini can know, literally.

"In two days I'm going to war," he said. "I think about nothing but the fight. It eats away at me and I try to keep a little calm, but not too much."

The sort of furious adrenal edge known best to foot soldiers will be a part of boxing as long as it exists. Death, and the fear of it, is the dark basis for the fighter's wide eyes.

One of Duk Koo Kim's handlers found several Korean characters scrawled on the fighter's lampshade before his final fight. Translated, it read, "Kill or be killed."