Pittsburgh ? Jerome Bettis is one of the Top 10 rushers in NFL history and has gained more yards with the Pittsburgh Steelers than anyone except Hall of Famer Franco Harris.

When training camp opens Friday at St. Vincent College in Latrobe, Pa., all of that will mean nothing.

Just like the numerous rookies and free agents in camp, Bettis will be competing for a job. A job that, until now, he has done better than all but a handful of runners in NFL history. A job that, until now, was assured as long as he was healthy enough to pull on his No. 36 jersey.

Bettis has rushed for at least 1,000 yards in all but one of his seven seasons with the Steelers and his 1,207 per-season average is the best in team history.

But he wasn’t healthy at the end of the last two seasons. As a result, he was a non-factor when the Steelers were eliminated by New England in the AFC championship game after the 2001 season and by Tennessee a round earlier last season.

Coach Bill Cowher challenged Bettis to prove he could get into shape and be the runner he was from 1996 until the second half of 2001, when a groin injury cut short his season. Last year, a knee injury that required an offseason operation was the problem.

Despite being pleased with the lighter Bettis he saw in spring workouts, Cowher is continuing to challenge him. The coach is refusing to call Bettis a starter, insisting he must win the job from the smaller but quicker Amos Zereoue, who outgained Bettis 762-666 last season.

“We will switch them up and give them a chance to run with the first team,” Cowher said. “We will give them both a chance to run and see how it unfolds and go from there.”

Bettis was threatening to win his first NFL rushing title when the groin injury hit in 2001. Last year, despite missing a quarter of the season because of a sore knee, Bettis averaged 63 yards in the games he played from start to finish.

Cowher noted that the NFL was a what-have-you-done-for-me lately business, and Bettis apparently hadn’t done enough during the last 11/2 seasons to justify being handed a job without having to work for it.

Pittsburgh running back Jerome Bettis (36), seen in this file photo, has struggled with injuries the past two seasons, and the Steelers aren't guaranteeing the standout a starting spot.

Tight end Mark Bruener, whose last two seasons also were cut short by injury, found out the same thing.

He was scheduled to make $2 million this season, but the Steelers told him he could accept an incentives-laden $750,000 salary or be released. He chose to sign for the lower salary and compete with Jay Riemersma to start.

“There is nothing wrong with people being challenged,” Cowher said. “We are all being challenged. I am being challenged. I don’t care what you have done, it has no bearing on what you have in front of you and what you have to do.”

That’s why Cowher thinks Bettis will respond to the competition of camp. Bettis is 10th in NFL career rushing with 11,542 yards, and would move six places past Tony Dorsett into fifth place with another 1,198 yards — until two years ago, an average season for him.

“The great ones … when they have been challenged is how they have become great,” Cowher said. “The challenges from the outside aren’t as great as the challenges they put on themselves. The great ones are challenging themselves.”

Among the other runners on the Top 10 list, Emmitt Smith, Walter Payton, Dorsett and Harris all had 1,000-yard seasons when they were as old or older than Bettis, and Marcus Allen gained 4,968 yards after his 30th birthday.

However, none was as big as Bettis, a power runner who gains most of his yardage in traffic and thus sustains more contact than those with a less-physical, run-it-wide style.

“As long as I’m healthy, I’m not worried,” Bettis said.