O.J. Simpson's left arm was pink and ragged where the Astro Turf had chomped it up. His right arm had a bandage on it. He sat there in his shorts, with his hands over his face, trying to remember what a philosopher had said.

"It hit me like a ton of bricks," Simpson said. "'Fame is a vapor, popularity an accident, and money takes wings. The only thing that endures is character.'"

That was the quote, or something like it, and Simpson looked pleased. "You learn, I think, early," he said, "that - I don't know - class will prevail."

Ever since he descended on the University of Southern California a decade ago to set 13 records in two years and walk off with the Heisman Trophy, Simpson has signaled over and over that it is possible to attain the heights and do it with unflappable grace. It is possible to hustle your way out of the projects, possible to be a black scholarship student politely signing autographs in front of a Saturday Evening Post writer who will go home and declare inprint that the American dream now has a guaranteed future.

Orenthal James Simpson came home last spring, really, when Joe Thomas, the general manager of the 49ers, announced that the Buffalo Bills had traded Simpson for five 49er draft choices. Simpson's age (31) and his left knee (occasionally lame) hardly dampened anybody's enthusiasm.

Eight games into the season, with the 49ers' record at 1-7 and a game Sunday at RFK Stadium against the Redskins, much of the fanfare that accompanied Simpson's homecoming has disappeared.

He has scored only one touchdown, been over 100 yards in a game just once and, while his 532 yards ranks seventh in the NFC, his 3.8 rushing average is not sensational.

"I have to realistically know that I'm at a point in time at my age that it (his career) comes to an end," Simpson said. "And it comes overnight." He snapped his fingers and leaned back in his chair. "If it hits me in the middle of the season, I'll be prepared for it."

When it comes, it will end a phenomenon that began (or so the story goes) when this brash San Francisco kid walked up to fullback Jim Brown at an ice cream stand after the Cleveland Browns had finished dismantling the 49ers. "You just wait 'til I get up there," the kid said. "I'll break all your records." He didn't get them all - Simpson still has not broken Brown's career record of 12,312 yards - but by last year he had leaped, dodged, and speinted his way to 10 other National Football League records, including most yards for a season and for one game.

"That other world is going to leave, anyway," Simpson mused. "You know, they say the roar of the crowd is just a loud echo. It's going, anyway. So I have to prepare myself for something I think I can do . . . when I leave the football field, obviously, my appeal will be a little different than it is as a football hero. I don't know if I'll be as actively pursued as an endorser. Now I have the luxury of turning down tons of deals, you know, for great deals of money. In four years, I don't know if I'll have the luxury of turning down anything."

On O.J.'s 30th birthday, he sat down with his lawyer and his tax man. "As a kid, I always had phases in my life and 30 was the first big phase in my life. I had written down when I was 21 - when I finished USC - I had written down where financially I hoped to be, and I hoped my house was paid for, and at 30 I wished I had amount of money in the bank, and I'd like to have two kids . . ."

He got the salary, currently $730,000 a year, and a house in Los Angeles, and a condominium with view in San Francisco. He got the children (there are three now; Simpson recently separated from his wife). He got movie roles, television work, business deals that include a chain of racquetball courts, and product endorsements so familiar by now that a lot of people think O.J. Simpson is that handsome fellow who leaps over obstacles at airports and drinks orange juice with glowing children.

He talks about Joe DiMaggio now, the king of the graceful exit, the way he used to talk about his hero, Willie Mays.

"I think people are still in awe of Joe DiMaggio" Simpson said. "I think if Joe walked into the room, it's almost Mr. DiMaggio, you know. He became bigger than his talent on a baseball field. And I like that.

"I don't want to disappear. I do like the notoriety. When I was a kid, I always felt that it was one of the bigger motivating things for me. I loved the fact that people used to gather around Willie Mays and stuff, and you know, talk about him being a celebrity. I loved that people would look and say, hey, there goes somebody. I know when I was a kid on Potrero Hill I used to say, 'Some day when I walk down the street, they're gonna know who I am."

They do, of course. They mob him for autographs, embarrass him by taling about newspaper photographs of Simpson dancing with ladies he never met, scream "JUUUICE!" the minute he trots out onto the field at Candlestick Park and yell at him from the cable car as he carries his laundry down from his new apartment in the city.

It is his place in the locker room that he will miss most, Simpson said finally. "When you walk into that locker room, I don't care what a guy's religious belief is, I don't care if his IQ is 180, I don't care what his major was, what his political beliefs are. It's the man who puts it on the line. I mean the guy who is strong inside, that's the guy they listen to in the locker room."

And he will also miss the simplicity of a world free of moral mush. "Football is such an absolute. There's a winner and there's a loser. Either you did your job or you didn't do your job. You know, we sit in that room, and look at the film, and hey, there it is, in black and white, in front of you. You see who screwed up and you see who did their job and you see who did more than they were supposed to do - because everybody knows the other guy's assignment. It's the challenge, the clarity of the whole thing. It's something I'll miss quite a bit . . ."