A short toss from where the slow, grand confluence of the Allegheny and the Monongahela forms the Ohio, Franco Harris makes his slow, grand way through another Steeler practice at Three Rivers Stadium. It is a wonder he can move at all.

The steel mills pump the sky full of gritty smoke, the air is damp, ochre, oppressive. What's more, Harris is 33, and 20 odd years of football practices and an infinite number of bracing shots to the viscera can bring a guy to say, "Thank you, but enough already."

But at an age when most running backs have long since hunkered off to Leisure Village, Harris is chasing down Jim Brown's career rushing record. With 106 yards against the Patriots Sunday, he passed O.J. Simpson on the all-time list and now has 11,309 yards, just 1,003 short of Brown's 12,312 yard total. Late this season or early next, health and fortune permitting, Harris should take the lead.

Not everyone is enchanted with the prospect. Even Harris admits his numbers cannot compare to Brown's. Harris is in his 12th season; Brown retired after nine at the age of 29. Brown played four 12-game seasons and five 14-game seasons for the Cleveland Browns; Harris has played six 14-game seasons, four 16-game seasons and last year's strike-shortened nine-game season. Brown's per-rush average is a full yard better than his pursuer's though his offensive line was not nearly as efficient.

For some, the difference is deeper still. Brown's running mate in Cleveland, Redskins Assistant General Manager Bobby Mitchell, says, "I don't think Jim would be too happy if it's Harris who breaks it. Franco's had a tremendous career, but in no way, shape, form or fashion is he near Jim Brown.

"He has none of the things Jim Brown had, not the speed, the tenacity, the strength. He doesn't even have Jim Brown's ability to catch the football, though he catches it well. Not one thing he does is as good as Brown. It's mostly attributable to the team. That's a hell of a team they've had over there."

In the 12 years since Harris graduated from Penn State and came to Pittsburgh, his detractors, including former teammates such as Preston Pearson, have accused him of "running for the Gatorade," of tippy-toeing to the sidelines before the defensive behemoths can bash him to the earth. Harris is an anomaly in a fullback tradition rich with men whose greatest delight is pain. Where an Earl Campbell relishes the prospect of making cleat prints on the spines of defenders, Harris will step out of bounds and harm's way if he sees no prospect of further yardage.

In practice, Harris is even more cautious. He goes through his paces and routes deliberately, the way a sprinter might walk off his distance, checking the track for angles and banks, the nuances that might be of subtle significance when the real event is at hand. He is not even physically impressive. With a 4.8 time in the 40-yard dash, Harris is slower than many linemen and his arms are saplings in a league thick with sequoias.

In a break between meetings and afternoon workouts, Harris makes time to talk though ordinarily he would rather wrestle gators than submit to interviewers. Weariness and not a little pain are obvious in his gimpy carriage. His broad, placid face looks a little drained.

"I've always thought I've worked hard, but people have always thought I didn't," he says. "It was never a conscious thing to run from sideline to sideline, but when the play takes me there, and there are guys there waiting for you and there's no more to gain, I see one option. Anyway, there've been a lot of players hurt going out of bounds. As a matter of fact, some guys let up when they go out of bounds and defenders really go for your legs.

"Your career can end in one play.

"Earl (Campbell) gets hit directly, but I've always been a great fan of O.J.'s. When I watched him, he'd never take a hit directly, He'd always slide to one side. It's my natural instinct to want to slide and not take an extra hit."

After such an explanation, it's hard to see why otherwise reasonable men would try to run over a linebacker. Simpson, for his part, says, "I'm happy for Franco, we're friends, but I never looked at him passing me as making him a better football player. As far as his style is concerned, everybody respected Larry Brown. No one ever questioned his guts or his tenacity. But Larry hasn't played in seven years. And on third and one, Franco doesn't step out of bounds. You know, he's a little like fighters like Ali. When he got old, he knew when to cover up. Maybe if Tommy Hearns had known how to do that instead of being Mr. Macho Man, Sugar Ray would never have knocked him out."

For five years the Steelers rode Harris to success, then turned more to a mixed attack as Terry Bradshaw matured, and now have returned to the run as Bradshaw ages. Art Rooney, the man who bought the Steelers franchise for $2,500 in 1933, walks the paneled halls of the Steelers offices, ruling with his sons a team that ranks with the Packers, Yankees, Canadiens and Celtics as the finest in American sports. Rooney's enthusiasm for his fullback is deep and paternal.

"The fellow we were highest on in that draft was Robert Newhouse. He looked strong," Rooney says of the squat, dependable runner, now in decline with the Cowboys. "But our scouts liked Franco. Glad they did."

Coach Chuck Noll was unimpressed by his new runner in their first training camp together, but Harris' qualities as a fullback with finesse were soon evident, earning him AFC rookie of the year honors and a trip to the Pro Bowl. "He's done all I've ever asked him to do," Noll says. "There's no use comparing him to Brown or O.J. Why bother?"

"What Franco is, is a fullback who runs like a tailback," says Bradshaw. "He doesn't have O.J. or Jim Brown's speed, but he's quick and he excels in big games."

Harris' career has been an unending stream of big games. The Steelers had been losers for the eight years before Harris arrived; they have been winners ever since, with NFL championships in 1974, 1975, 1978 and 1979. In 1972 Harris starred in the most dramatic highlight film ever, the so-called "immaculate reception" of a defelected pass that beat Oakland, 13-7, in the waning seconds. In Super Bowl IX he broke the Super Bowl rushing record with 158 yards, leading the team to its first championship, a 16-6 win over the Vikings. No one in NFL history has carried the ball as many times, and in the last eight seasons he has missed only five games.

"But the thing about Franco is that he doesn't just survive, he performs," says Joe Greene, his former teammate. "He looks like the same old Franco to me. He's always thinking out there. His way is to slow his mind down to react to what's there. That's why he gets most of his yards in the second half. He's had a chance to see what's going on in front of him. Never changes."

Harris pushes away the subject of retirement as though it were a plate of bad food. "You know, in the last couple of years, I've felt stronger," he says in a Steeler meeting room. "I never came in thinking how long I'd last, and I don't want to think about it now."

As the fuzzy-cheeked inheritors of the Steeler legacy file into the room, Harris goes over the old team's extraordinary record and a lineup that reads like an all-star list: Lynn Swann, Greene, Rocky Bleier, L.C. Greenwood, Mike Webster and Dwight White. "Whew!" he says. "That's the greatest thing to look back on. If I do get old. If that ever happens. I was part of the greatest team there ever was.

"I'm sure (retirement) will come over something physical, maybe mental. It won't have anything to do with records. If I ever get the opportunity to break Brown's record, it'll be, 'Where do I go from here?' I just want to keep working."

For nine years, Harris roomed with Swann, until last year a balletic wide receiver with the Steelers and now a broadcaster with ABC. "How can anyone argue with anything Franco has done?" Swann says. "Twelve years. Four Super Bowls. I don't know when he'll stop. He never talks about it that much. He'll let you know when it's time to stop. Franco has always been one of the quieter people on the team. He's like the iceberg--he only lets you see a little part of him. See, Franco sloughs everything off. Knocking him is like throwing water on the Great Wall of China. He's still standing, ain't he?"

For Harris, questions about records and retirement are deeply personal, and questions more probing than that are met with embarrassment. Harris bids the clutch of reporters good-bye and eases back in a plastic chair for one more chalktalk. He looks bored. Five hours left in the workday. Days until he starts chasing Jim Brown again.

"You know Franco's usually the last one to practice, doesn't see much point in hanging around the locker room," Art Rooney says. "But he's the last one to leave. Just yesterday I went out on the field and everybody else had pretty much gone home. But there was Franco, still taking his laps. So I asked him, 'Twelve years here. Aren't you in shape yet?' And he said, 'I still have a little way to go.' A little way to go! Can you imagine that?"