Robbie Bosco's arm apparently is OK, but unfortunately his back isn't.

Bosco is one of six quarterbacks competing for three spots on the Green Bay Packers.The former BYU All-American quarterback, who led the Cougars to the national championship as a junior in 1984, missed his first two pro seasons because of arm problems. A Packer spokesman said this week that Bosco's arm problems seem to be a thing of the past. "He's throwing acceptably. He's actively competing for the job of quarterback."

But he's missed the last three days of practice because of an injured back. That included a scrimmage Friday, where coach Lindy Infante got a look at four of his six quarterbacks as the Packers wrapped up their first week of camp for rookies, free agents and selected veterans.

"He called and told us he pulled a muscle in his back," Elva Bosco, Robbie's mother, said in a phone conversation from her home in Roseville, Calif., Friday night. "He tried throwing again right after he hurt it and aggravated it."

Among the quarterbacks Bosco is competing against is another former BYU All-American, Marc Wilson. The Packers signed Wilson after the Los Angeles Raiders waived him. Other quarterbacks on the Green Bay roster are Don Majkowsi, Blair Keil, Bud Keyes and Randy Wright. Wright, who shared the starting spot last season with Majkowski, also missed Friday's scrimmage with an injury.

*** Another ex-BYU player whose career has been dominated by injuries, was injured again Friday. According to wire service reports, Todd Shell, San Francisco 49ers linebacker, suffered an apparent bruised spinal cord during a controlled scrimmage and is expected to be out for at least several weeks, the team said.

Shell was taken by ambulance to Roseville Community Hospital after lying motionless on the field for several minutes at the 49ers' Sierra College camp in Rocklin, Calif.

Coach Bill Walsh said that although there was a numbness in Shell's extremities, he is expected to recover fully.

Walsh would not speculate on how long Shell would be out, saying it "could be the season or it could be two months."

Shell was coming up to make a play and was blocked by tight end Ron Heller.

"He just met a blocker (Heller) with his head down and it was snapped back, and he suffered the bruise on his spinal column," Walsh said.

For Shell, 26, a fifth-year veteran, it was another sad chapter in what has been a history of injuries.

He has missed numerous games due to injuries in his career and spent nearly all of the 1986 season on injured reserve after injuring a quad muscle in training camp and all but the final two games of the 1987 season after tearing ligaments in his left knee in the final preseason game against Seattle.